Soul Calibur III - YES
Despite the balance issues previously mentioned, this game is a lot of fun, and I find it just looks and plays a bit better than Soul Calibur II. Plus, I made the best character I've ever made in a Create-A-Fighter mode in this using Saint + Soul of Sophitia. And we made some terrible crap too. If Dr. Wilhelm sees this...Remember Danny? XD
Metal Slug 4 & 5 - NO
Metal Slug Anthology is out, and even though it's expensive, it's definitive. As much as I love these two games, just go buy Anthology if you've got the scratch.
Jojo's Bizarre Adventure - YES
I own the PSX version, which suffers from some load times, but overall the core game is basically untouched. I like this game a lot, and picked it up for 3 bucks at my local EB Games. Fun game all around. Something to break out when you're just like "let's play something we haven't played in a while," or "let's play something totally feckin' weird."
Phoenix Wright 2: Justice For All - YES
I cannot stress this enough, everyone must at least play these games once, full way through. This is the game that makes me wish the genre of Hot-Blooded Lawyer Action was established further than this game series. Hopefully Harvey Birdman for PS2 will be like the Ace Attorney games.