I have fond memories.
I remember seeing early screenshots in an issue of GamePro for Sonic Adventure, and saying to myself that there was no way that games would look as good as Sega was advertising. Flash forward a year or so later, and my buddy fired up his Dreamcast with said game in it for me to see. At that time, I was a believer.
We played so much on his system. Sonic Adventure was a decent game, but once I got past the "wow" factor, there wasn't too much to write home about. But it's sequel, the cleverly titled Sonic Adventure 2, was a huge step up. Playing versus mode against him day in, day out for hours was a blast. We made fun of the cheesy music a lot, too. Really liked that game.
Phantasy Star Online is one of those titles you don't really skip when mentioning Dreamcast games. I played this for hours, and hours, and hours. I really liked the aesthetic of the title, and the music was really, really nice. Never had an internet connection for the machine, so I missed out on multiplayer, but the gameplay was fun regardless.
By a wide margin, one of the most-played titles on the machine by my reckoning was Marvel vs Capcom 2. I must've sunk at least a year of playtime into that game. I was terrible using the arcade stick on the coin-op, but I felt right at home using the Dreamcast controller. It was weird.
Resident Evil: Code Veronica remains a favorite of mine, despite the fact that I've never beaten the goddamn game. I really liked the 3D environments and even today it remains a very tense experience. Fun fact: Claire is voiced by Alyson Court, who also portrayed Loonette the Clown on Big Comfy Couch. Bricks were shat when I found this out.
I wonder at times if I am the only person on the planet who found Shenmue (and, by extension, Shenmue II) to be a completely underwhelming experience. Gameplay was slow and frigid, and the voice acting ruined my ears. At the time, bad voice overs in games never bothered me, but even then, holy shit. I give credit for the largely interactive environments, and the music, and the scope of the game is awe-inspiring, but beyond that, there really wasn't too much to write home about.
Having the huge boner that I do for anything pertaining to mecha, Virtual On: Oratorio Tangram was a huge wet dream. I had all but completely mastered the first game in the arcades, and Sega's announcement that this iteration was on it's way had me scouring every arcade in town for info on it's arrival. I never could find an arcade cabinet for the game (something I was later able to attribute to very low production runs for the game in America), and as such, had to rely on the Dreamcast iteration of the software. Gameplay was fast and tight, the game looked incredible, Hajime Katoki's mech designs were made of love and joy. My complaints were minor, such as oversaturation of particular virtuaroids; Did we really need three variants of Bal Bas Bow? Two versions of Apharmd?
I played through the first eight hours of Grandia 2, largely unimpressed (save for Ryudo, whose jackassery proved hilarious). It was a uniquely competent game, featuring a compelling battle system, nice music, some interesting characters, basically all the trappings of traditional RPG's, but for whatever reason, I've never been able to fully invest myself into it. I have a copy sitting in my closet. I'll load it up one of these days and see it through to the end.
Skies of Arcadia proved to be a completely compelling experience. Pirates are such an uncommon element in video games, especially as playable characters, so from the get-go, I was entranced. I liked the characters and the battle system was fun too, if a little easy (What's that? Random battle? "Fire Consume my enemies . . . ").
I feel compelled to mention Industrial Spy: Operation Espionage as perhaps the shittiest game I played on the Dreamcast. It looked so cool! Anime styled art and an MGS-like stealth premise? I'm there! Fire up the game, and its' mediocrity is engulfing. Stock techno music serves as the aural backdrop to the title screen, like someone just hit you in the face with his Casio keyboard, and then the game just lays some truly rock star gameplay on you. It defies description with the kind of zeal you'd expect a starving kid to attack a sandwich with. If you bring this game home, your dog will bite you.
How about Chu Chu Rocket? I couldn't believe how fast paced that game was! My buddies and I popped it in for the first time, not knowing what to really expect. 3 seconds into our first game, we are freaking the f--- out, mice are running everywhere like they got ADD or some shit, it's two in the morning, and we're trying our damnedest to not burst out laughing and wake his parents up (which of course only makes us laugh harder).
And of course, Space Channel 5. Such a goofy, bizarre game. I was never able to get the hang of the "Simon Says" style gameplay, but you just don't see too many games with that level of character. Full of innocent charm! I loved it. Killer soundtrack, too.
There are titles I would love to spend more time with, too. Jojo's Bizarre Adventure, Jet Grind Radio, Tokyo Xtreme Racer II, various SNK fighters . . . .