They had this really clean high-res, high-poly look and nice colours compared to the more blocky and blurry looking fighting games on the PS2.
I've been messing around with DOA3 and DOA2U on the XEMU emulator and the resolution here is upscaled 3x so what you're seeing is definitely a lot sharper than it would have been on original hardware, but still. Blown up like this it you could tell me this was a PS3 or Xbox 360 game and I'd believe you.
As much as I like the series for its gameplay and as nice as I think the Xbox games look I've always thought that the weakest part of the DOA games has always been their incredibly bland character design and artstyle. Even though they draw from the same pool of martial arts archetypes and stereotypes as every other fighting game series in existence pretty much every character is much more lame and feels less interesting than their equivalents from Tekken, Street Fighter, etc. Kazuya Mishima has more character in his eyebrows than the entire roster of the DOA franchise.
The female cast is supposed to be the draw 
but on balance the designs aren't that much more hornier than most other Japanese fighting game franchises and the characters in those tend to have some personality to go with the fanservice.
I had my mind thoroughly blown by the bump maps, bloom and limited dynamic shadows in Halo 2 even if in retrospect that specific transitional period with blocky low poly assets with sort of advanced effects hasn't aged all that well
From the perspective of someone who doesn't really know how to play fighting games, DOA has always probably been my favourite in terms of playability since even if you're not super good the simple inputs, wall splats, interactive stages and plenty of moves that send your opponent flying halfway across the screen generally make you feel cool