Agreed, the overlays/backdrops certainly make some games look incredible. Again, performance seems to be greatly affected on my setup tho
Just wanted to add a note on performance here for those who are not totally immersed in MAME.
Several recent changes have affected MAME's performance.
First, alpha-blending (transparency effects) has been added to many drivers.
Also, the new artwork appears to be redrawn with each screen refresh, slowing performance.
There was a move from sound samples to discrete sound emulation, which slows performance.
Also, the method of "blitting" to the screen was also changed and 8-bit color modes were dropped.
The net effect of this is that more complex games should be faster, while older and simpler games may take a significant speed hit.
The ideal solution would be for MAME to use less sophisticated routines for older games and more complex routines for newer ones.
Why doesn't MAME do this?
Here's my opinions:
First, MAME is not really designed to make the games play as fast as possible on as minimal hardware as possible. It is designed for accuracy and realism to the original arcade board.
Next, MAME is designed for portability (there are versions of MAME for cellular phones and digital cameras) and expandability (it wouldn't support 3,300 games if you had to choose which core functions to use with each game).
Finally, if you are a MAME dev and writing code for MAME, you probally don't sweat spending $1000 for a 2.2 Ghz processor, 512M of Ram, 128M GeForce 4 Ti 4200 video, and 7200 RPM harddrive. (I can't blame them). And if the above is your development system, you may not notice that Pac-Man doesn't play very well on a Pentium 90 anymore.
In closing, before you take the above as pure jealousy, there is another justification for supporting the more complex games: If your 2.4 Ghz Pentium 4 isn't fast enough to play Stun Runner, there's not much you can do. If your Pentium 90 won't play PacMan, you can always upgrade or use a previous version of MAME. Therefore, it make sense to optimize the most complex games to get them playable on near-current hardware.