Too much money circling around the world made Barter (1, 2, and NV) and Gambling (1 and 2) feel unnecesary. Sure, it would be really fun to role-play as a Traveling Merchant or as a Degenerate Gambler or whatever, and be able to bribe your way into the endgame (Lanius, my man, listen, I have enough money to finance your next campaign, but only if you and your troops leave the Mojave for good). Or maybe you could hire some mercenary/paramilitary group to help you win battles even if you have no combat skills whatosever (weak goons would be cheaper, while seasoned soldiers/hitmen would be far more expensive, especially considering they'd charge you by the hour, making this strategy impossible for a non-money oriented build). Thing is, the amount of money and valuable loot you get from even having <15% Barter is massive so building a Merchant/Gambler class feels like wasted skill points.
Too much ammo makes the crafting system in NV feel redundant. If you had only enough ammunition to fight one or two battles before running out of it, then the crafting system would be a must-use for anyone who isn't some sort of sharpshooter who makes efficient use of each bullet. Didn't invest enough skill points in Repair in order to craft your own ammo? No problem, try getting a companion with a mid/high Repair skill. Can't find a repairman companion? No problem, go to the local workshop and pay the craftman to make some for you. Now, you could say that this would turn Fallout into a survival sim or something like it, which is not what Fallout is. But it's the only way I see a crafting system would make sense in a Fallout game.
Too much stimpaks make any Medicine/Doctor skill feel unnecesary except in the early game. Again, it would be amazing to role-play as a Field Doctor who keeps his/her companions and mercenaries healthy and buffed (shall I say drugged) for the battle (anyway, that's how I lost my mezical license). Maybe, the better Medicine skills you have, the most chems you can give to your companions and mercenaries. So even of you had a small crew behind your back, just pump them Psychos, Buffouts and Turbos in their veins and send your own super soldiers to the battlefield. But yet again, none of the games give you the gameplay possibilities to do that. Good luck trying to beat an Enclave squad while you are a support medic instead of the spearhead of your crew.
Maybe we're asking too much? Or maybe I'm just stuck in the same build over and over. I guess my point is, one of the big gameplay flaws I see in Fallout is the over-aboundance of resources, which hinders the role-playing posibilities and naturally always pushes you to kill and loot instead of using your skills. Anyways, all three games have pretty good RPG mechanics when we consider the actual circumstances the developers went through.
