The original Sonic Adventure was my favorite Dreamcast game. It was just presented so well, and was basically the attracting factor to playing the dreamcast.
Sonic Adventure 2 Crazy Taxi 2 Quake III Arena Rush Rush Rally Racing (<3) Giga Wing 2 And probably a lot more I cant remember atm.
This = Awesome. This is the best racing game on Dreamcast. Ever. Fur Fighter! Its just awesome, its freaking long (I never beat it! lol), you have lot of shit of things to do, lot of characters, freaking guns!, gun upgrades!, lot of levels, the average level time its like 45 min each one, and the music its just perfect. Also...best Dinosaurs ever. --- I'll recommend Capcom Vs SNK 1 and 2, Silent Scope, Soul Calibur, Biohazard Code Veronica, Shenmue and its sequel. Bah, almost every dreamcast game its worth for something xD
I'd say Sonic Adventure 1 (duh), Jet Set Radio, Skies of Arcadia, Power Stone 2, Toy Commander, Crazy Taxi, Fur Fighters and if you're really looking for some crazy, get some Seaman on the go. Damn that shits weird... Ah if only they made games like they did back then now. I might actually own something more current than a PS2 with one game.
I can only choose from games I own. Like Saturn titles, DC games were hard to find here. Shenmue 1 & 2 Metropolis Street Racer Ecco Defender Of The Future SA1 & 2 QIII Arena Soul Calibur MDK2 Power Stone Fur Fighters (a buggy game that I objectively speaking would not recommend, but I kinda like it.) Titles I wanted but never got my hands on: Crazy Taxi Jet Set Radio Power Stone 2
I can say a few: Sonic Adventure (Durr hurr) Power Stone Power Stone 2 (IMO, 1 was better, but that's an argument for another day) Sonic Adventure 2 I quite liked Centipede. Not necessarily the best of the best, but it kept me entertained for awhile. That's about all I can think of (I had some others, but not really enough to keep going).
You can check out the bleemcast! beta for Dreamcast as well. Though it is glitchy, it runs a good few PS1 games fullspeed. Also: Marvel vs. Capcom 2: The Dreamcast version is still my favorite port, since the PS2/Xbox versions were a bit sloppy and the PS3/360 version is chopped up (though with online, which is a big plus). Typical fighting, but it's still very entertaining. Street Fighter III: Third Strike: This port is nearly arcade-perfect as well (minus a few removed frames of animation). It has it's own arranged soundtrack and a few extra features. Sonic Adventure 1 and 2 for obvious reasons. Jet Set Radio: The game is incredibly unique and original and features THPS-esque moves and tricks as well as a crazy soundtrack. Also: GenesisPlusDC and NesterDCSE
Omikron I own, and it's like a PSX game Bleem'd. Also has fogging up the arse, and has loads of technical issues. It's good though. Death Crimson OX is subpar as a lightgun game, but totally playable. Extreme Racer is yet another racing game. Can I pitch in a vote for Half-Life Dreamcast? Or how about that dogfighting game? That had amazing 4-player multiplayer.
While Shenmue is by far my favorite DC title, you should pick up Headhunter. It's basically Metal Gear Solid + GTA, if you can wrap your head around that.
Shenmue I and II Power Stone 1 and 2 Crazy Taxi 1 and 2 Street Fighter III: Third Strike Cannon Spike SoulCalibur Maken X Rez L.O.L. - Lack of Love San Francisco Rush 2049 Tony Hawk's Pro Skater 2
Not saying its the best Dreamcasst game. But any one who likes Kart Racers should really try out that Looney-Toons Space Race. It had really nicely cel-shaded graphics solid tracks and items. Its probably my favorite kart racing game outside of the Mario Kart series.
More than anything else, I'd love to see Tech Romancer on Virtual Console. What an underrated fighting game with great character variety. Could have been deeper, but then again I can't talk because I never got good at it.
Obviously, the best Dreamcast game was Shenmue. Jet Set is close, though, along with Sonic Adventure.
I'm going to have to go with Space Channel 5 Part 2, Chu Chu Rocket, and the Sonic Adventure games. Those are the only ones that I've played.
The retail packages for Bleem! for Dreamcast (Metal Gear Solid, Gran Turismo II, and Tekken III IIRC) recently had their encryption cracked, too, IIRC. So you can make selfboot ISO copies.
Here's a couple recommendations from me: -The Sonic Adventure games - Jet Set Radio -Crazy Taxi - Fatal Fury: Mark of the Wolves - Fur Fighters (many technical problems, but fun nonetheless) - MDK - Rainbow Six - NFL 2K (Okay, American football isn't exactly popular outside the US and some parts of Canada, but this was a very fun game) There are many others of course (which others have touched upon), but this is the start of a good collection.