I tried it, don't really like it. It looks very messy and a lot of the things people have suggested (like a wishlist, clock, etc) they have ignored. It's nice they added achievements to some older games (HL2, HL2:EP1, Opposing Force, Peggle Nights..). Still, it needs a lot of work in my oppinion.
Well I like the look, but haven't had any issues as yet. Plus it is a beta, so I do understand it will have problems
Overall I quite like it, the old Steam UI does look a bit dated and hasn't changed much since 2003 I don't think. My only complaint is I think its a bit in your face, I don't think you can have the compact games list open anymore which is something i really liked. I thought achievements had been added to HL2, i didn't remember it having them the last time i played it.
The first screenshot you posted looks very nice, I wat to install when im home. I like how it appears to show the games your friends have recently purchased, good work Valve
I like that feature as well, talk about a great way to advertise other games. One thing I noticed last night while looking around through the Beta was the Mod's section has either been removed or is so hidden it's not easy to find. Having kids I ain't gotta lot of money so mods to existing games are usually a great way for me to get more life out of the games I do own.