If I were a first time player, I’d go “how do you build a fleet?  How do you fight with a fleet?  How do you handle its air support and move troops with it?”.  I mean let’s review:

Transport: Doesn’t participate in combat, (complicated transport rules go here)
Subs: 0.33 Attack, 0.17 Defense, and 0.17 HP per IPC.  (complicated sub/destroyer/aircraft interaction rules go here)
Destroyers: 0.25 Attack, 0.25 Defense, and 0.13 HP per IPC (detects subs)
Battleships: 0.25 Attack, 0.25 Defense, and 0.13 HP per IPC (can soak a hit)
Aircraft Carrier: 0.08 Attack, 0.17 Defense, and 0.08 HP per IPC (2 Fighters can land on it)
Fighters: 0.30 Attack, 0.40 Defense, and 0.10 HP per IPC (complicated landing rules, weird interactions with subs)
{Note that Carrier Groups as a whole have 0.22 Attack, 0.31 Defense, and 0.09 HP per IPC}
Bombers: 0.33 Attack, 0.08 Defense, and 0.08 HP per IPC (as Fighter but with superior mobility, weird interactions with subs)

Every single one of these units is important to naval conflicts, requiring you to carefully use them as a combined group.  And every single one of them costs 50% of more of any country save the USA’s income.  How precisely is this supposed to be “simple” or “open” to new gamers?  I’ve been playing/pondering Axis and Allies for years and its still easy to forget about the esoteric properties of units at inconvenient moments, such as forgetting that the reach of the Bomber lets it sink an undefended Transport and then land in some minor territory, or that a single Sub can wipe an unsupported Carrier Group 4/9s of the time.

If they really wanted to make the game simple, they should have done this:
Infantry: Attack=1, Defense=2, Movement=1, Cost=3 (land)
Armor: Attack=3, Defense=3, Movement=2, Cost=5 (land)(blitz)
Aircraft: Attack=3, Defense=4, Movement=4, Cost=8 (air)
Ship: Attack=2, Defense=2, Movement=2, Cost=6 (naval)
Fleets can transport/carry 2 IPCs worth of land/air units for each Ship in them.  Defending fleets can block 2 IPCs worth of land units from landing per ship in a sea zone adjacent to the invaded region.

Looking at the game, and having played/heard multiple sessions, outside of bad die rolls and extreme player eccentricity, its hard to see how the game does anything other than this:
1. Russia falls by Turns 3-5, generally depending on whether or not Germany diverts airpower to sinking the British fleet first.
2. The game enters a long boring stalemate where both sides trade Eurasian and Oceanian territories willy nilly before someone takes a capitol or dies trying.

This is basically because of two factors:
A: Because of the reduced IPC income, Germany can build 4 Infantry for every 2 that Russia does.  This gets ugly once you factor Germany having way more support units that ensure good exchange rates, Russia having no AA to counter those support units, and the Berlin=>Moscow march being back down to 3 spaces.
B: Because of the reduced IPC income, it takes longer for Great Britain/America to pressure Germany in Western Europe.  Great Britain generally has to build an Atlantic fleet, Atlantic transports, and ground forces in both the UK and India.  America generally has to build a Pacific Fleet, Atlantic transports, and ground forces to field in both areas.

The net effect is that Russia gets wiped out, whereupon the game trends towards a stalemate due to Russia being as subpar a reward as it was a threat to the Axis.  Even if all of Russia falls, its still only 28 Axis income to 27 Allies income, plus or minus whichever Eurasian and Oceanian territories have exchanged, but its hard to see either side getting the capacity to threaten the other’s capitols for a looong time.  Frankly, it amazes me that this game passed muster.  This game is supposed to be focusing on simplicity, yet “Russia will always fall” means the game is either broken if you assume “Russia falling ends the game” and is complex if you assume “Russia falling doesn’t decisively end the game” which is the case in pretty much every other Axis and Allies game.

Hence my suggestion that Artillery defend against Sea and Air threats, in addition to supplementing ground offense, while Infantry provide for more general defense against Land threats.

Interesting, that would mean that Tanks on the tip of the spear with M-Infantry would likely be exposed and fragile, but Tanks within the main force don’t suffer such.  Giving M-Infantry the Artillery bonus gives them a similar reward for being within the main force.

Anyone think that the Artillery, AA, and Blockhouse should all be combined into one unit?  Doing so would probably result in an increase in cost to 5, which would help balance the new Tank.

Artillery: 2-2-2-5
Powers
1. Gives +1 to an Infantry when attacking
2. Before the first round of a sea invasion, gets a potshot for 2 or less vs. landing units, casualties removed before rolling
3. Before the first round of any combat with enemy aircraft, gets a potshot for 2 or less vs. air units, casualties removed before rolling.

In this setup, I would also gives Fighters a potshot of 3 against aircraft, and Fighter-Bombers a potshot of 1.

@Brain:

Leave the tanks at 5, Allow mech inf to transport 1 artillery of 1 infantry with it. This would be good.

That is another acceptable fix.

The central problem is that Mechanized Infantry being a 1-2-2-4 unit makes it near strictly weaker than the 3-3-2-5 Tank, but the Tank is already well balanced with everything else.  The solution is to make the Mechanized Infantry balanced.  If it turns out that the superior movement is more powerful, then even then, the Tank only needs a marginal decrease.

Ways to improve M-Infantry
M-Infantry is a 1-2-2-4 unit that can transport 1 Infantry with it when it moves two.
M-Infantry is a 1-2-2-4 unit that receives +1 from Artillery
M-Infantry is a 1-2-2-4 unit that can be transported like an Infantry could (hence you could transport a M-Infantry and Tank)

Ways to marginally weaken Tanks
Tanks are now a 3-3-2-6 unit
Tanks are now a 3-2-2-5 unit
Tanks are either one of the above but receive +1 when working with a Dive Bomber

@Brain:

i think that the mech infantry is mainly for getting infantry to the front lines

Which is interesting given that they have no such power.

@bugoo:

But oh noes, the dreaded AA gun is in Berlin!  This may be true, so lets up the numbers to 3 carriers for 6 fighters.  You will lose 1 on average, so by round 2 you took 10 attack rolls at a 3.  With your bombards you would get 9 cruisers for that cost, or 9 attack rolls at a 3.  As the combat progresses, the carrier/fighter combo continues to outperform your bombardments!  Now yes I know AA gun rolls are dicey, so are bombard rolls.

The vital aspect is that Bombard resolves before units fire, which means that you don’t simply inflict losses, but you deny them a chance to inflict them as well.

Lets compare a Cruiser to a Fighter when attacking France (which WILL have an AA gun).
Cruiser has a 1/2 chance of inflicting one loss, usually just 3 IPCs, and eliminating that unit before it can fire is usually a 1/3 chance of inflicting 3 IPCs worth of losses.  Hence, each Cruiser deals 1.5 IPCs worth of damage and blocks 1.0 IPCs worth of damage.

Fighter has a 1/6 chance of being shot down, causing 10 IPCs worth of losses, and then has a 5/12s chance of inflicting 3 IPCs worth of losses.  Each subsequent round, it has a 1/2 chance of inflicting 3 IPCs worth of losses.  Hence each Fighter on average incurs 1.66 IPCs in losses and inflicts 1.25 IPCs in damage first round, 1.5 IPCs in damage each subsequent round.

Cruiser: 2.5 IPCs, weighting it by 10/12s gives 2.083 IPCs
Fighter: -0.41+1.5x IPCs, where x is the number of rounds beyond the first.

Hence, for Fighters to be worth it, combat has to last at least 3 rounds.  Also note that the Cruiser carries no risk of suddenly having a weaker air/sea force, which could leave one exposed to a counter-attack.

Granted, the fire first has been removed, and as such, they should probably lower the Cruiser’s cost to 10.  But in AA50, it was understandable.

That might work.  Mechanized working with Artillery allows it to compensate somewhat for its pathetic offense, Tanks and Dive Bombers both getting +1s makes them an extremely powerful attack engine.

With the defense oriented Mech Infantry, you actually have the manpower to do a second attack, allowing you to push forward twice in a turn, something that is quite useful, but you can only do it with the more expensive ground units.

Doing so pushes both the M-Infantry and Tank to the “useful” range without changing their costs.  Granted, it completely changes the nature of ground combat, as you have twice the threat range.

One possibility would be to keep the new 6-Tanks and 4-M-Infantry, but add a Blitz rule

Blitz: During the first round of combat, Mechanized Infantry and Tanks fire before other units do, and casualties are removed before other units can fire.

Doing that might make both M-Infantry and Tanks on par with Infantry, Artillery, and Aircraft, at least by the standards of previous maps.

There is the open question of how much bigger the map is, and whether or not units would actually need to use that mobility.  If so, that can justify the M-Infantry and Tank, which are balanced relative to each other, being weak compared to Infantry/Artillery.

Also, the more I think about, the more I wonder about how effective M-Infantry is in general.  Their defense is less than a Tank, their durability is marginally better, and their offense is weaker than that of Infantry!  In the mean time, they can’t be transported readily and they can’t be boosted by Artillery.  Their only advantage is being a better hit-soak than the Tank, and that only works so long as the Tank either has a cost increase or defense loss from its Revised version.