Okay, I had been having problems for over a year with my first, original ps2 - disc read errors, some dvd/games that wouldn't work, and frequent disassemblies to try to remedy the problems.
A couple of weeks ago, I finished with a ROUGH week of finals (senior in college) and wanted to get some games to celebrate. I went Saturday morning the day after finals and bought Resident Evil 4 and Gran Turismo 4(the game I was really after). I stick GT4 in, and the opening movie was going like 1 frame every 10 seconds and the disc was making a bunch of noise. So I figured I had to take it apart again and readjust the white dial that changes the lens height because it wasn't able to read the disc properly. The top cover of the playstation slid off my desk while I was working on it and pulled the power/reset ribbon cable out of the socket - so I had to fiddle a while to get that back in. Then, the controller/memory ribbon cable came out of the socket, and I fiddled with that for a while and could never make it go back in.
Finally, I said SCREW trying to fix this, I'm getting another playstation. Although, I didn't drive back out that weekend to get another one, so I had two new games just sitting there doing nothing until Monday afternoon after work. Surprisingly, I had to look at 3 different stores before I found a slim Ps2.
I've been using it for about a week, and I LOVE IT. It plays all my games, DVDs, its quiet (no noisy PSU fan anymore), I think it seems to load games slightly faster, AND it has a built-in IR sensor - I hadn't heard anyone mention that in all the reviews I read, but this is a GREAT feature - you don't need that bulky thing that takes up a controller slot anymore to use your DVD remote - and you don't have to reconfigure anything. Oh, AND it has a built in network adapter - I'm glad I didn't waste money on one for my old ps2. Also, I set up the network adapter with zero difficulty.
I've heard the top-loading disc tray being considered a disadvantage. I disagree. Less moving parts - less possibility of malfunction! The lens is exposed for easy cleaning (or damage, so be careful). I think this design works for longer - just look at how long portable CD players work vs. bulky stereos that have ejecting cd trays. My past stereos always skipped during songs or wouldn't play it all, but he ol' discman always worked better.
Also, no hard drive capability. From what I've heard, the hard drive is really only having if you want to play FFXI, but that game costs like $12 a month or something and I've heard it's not that much fun anyway.
One other thing, I think I've read that the slim ps2's are difficult/impossible to mod. Not an issue for me, but maybe that would bother some people.
I love this thing!!!