Which parts made you 'what'? lol. 
I'm not sure if you've read it but i have previously written my first impressions of XIII on my blog (here), and a short blurb about the podcast (here).
Of course as i have not had a great deal of time with XIII also (maybe 20 or so games total) it is difficult to form a solid opinion about the game.
From what i have played so far it is a good game spoiled by some things (for the most part glitches, Raiden, etc...). I actually quite like some parts of the system, it's the direction i had hoped the game would go after XII.
For the most part the problem with myself personally comparing the two games (preferences between the two), is that 02UM is accessable now and is familiar enough for me to understand (for the most part) what is going on.
I don't think that XIII has gone to the extreme of some of the newer fighting games (come back systems, etc) but when you look at the perspective of difficulty in terms of high damage combos (or landing them) i think 02UM had it right and that XIII veers in between the fine line of whether some combos might be a bit too easy.
When the game comes out and i get more access to learning it of course my opinion of it may change, but for now out of the two my preference is with 02UM.
Also the thing with 02UM is there is so much to learn within that game i think that i could play it for a long time to come.
As for the game overall i think (and hope) that it will do well in the West, i have heard people are playing 02UM over XIII in Asia, but i think XIII has a lot more 'appeal' compared to the older games.
The part that made me go what was probably "I've been waiting for a good kof since '98." I know most kof players might have that opinion, it was just a reminder of how I might be one of the few who even likes the "bad" ones, like '01 or XII.
I'll have to do my own assessment when the game actually comes out, but from the videos I've seen, it feels like XIII gets underestimated because most of who you see is K', Raiden, Elizabeth, Kula, Shen, and most of the rest of the cast falls by the wayside, and I can tell from some videos that in the right hands and with the XIII systems, the entire cast can do some great damage (Kane's Chin or Infinite's Duo for example)
02UM is really a great game, which I'll still play even if XIII really gains popularity in the West, but like Kane mentioned in one recent podcast, some characters are really favored by the 02UM system in XIII, and others are kind of just there. How most if not everyone can take equal advantage of XIII's systems (from what I've seen), gives a lot of characters the chance to dominate or just be played. When I went through a peliminary run of characters in 02UM, I could tell there were characters that I probably wouldn't be going back to outside of random, and not just because they weren't my style.
One thing I'll give you about 02UM that I forgot to mention before is how you can tell the skillset of a player based on what they can perform. Things I'm still trying to do that I've seen other pull off flawlessly does show a clearer level of skill. You're certainly right that there's a lot to learn in 02UM (glad to hear Foxy was actually getting some high(er) level play), but I hope most people don't read into what you said about 'how many actual different characters in the game, between the ones with the fireballs/anti-air or grapplers' (paraphrasing you) and dismiss some characters as being too similar.
I'm hoping and thinking XIII will have almost as much depth as something like 02UM has based off of the EX abilities, and some of the things we've been hearing from JPN players (different block-stuns for most characters), but like you, I'm waiting to see too.
