Tony Hawk Pro Skater series (PS2, GCN, XBX, PS1, N64,)
There would be nothing better than manualing and reverting in glorious HD. Activision could have the perfect moment to reboot this once-popular and now-faltering franchise with a downloadable game that remixes the very best levels of the original Tony Hawk titles. Throw in drop-in/drop-out online play, and you're golden. Even the later games in the series which introduced the ability to get off your board in order to reach otherwise difficult-to-access areas provided some fun to this dulling series. Who wouldn't want to see the birdman in crisp and clear HD?
Muramasa: The Demon Blade (Wii)
There were rumors that this retail Wii game was coming to the downloadable services of PSN and XBLA, but it was just that-- a rumor. The game already looks gorgeous running on Wii hardware, but just imagine how colorful and marvelous it would look in HD. Muramasa had players exploring the Japanese countryside, taking down mythical bosses like the giant Oni and Kraken. From the makers of Odin Sphere, Muramasa had little in the way of slowdown unlike its predecessor, so that wouldn't even have to be fixed. What we'd wind up with is a game that's exemplary in art design and as an art form.
The Legend of Zelda: The Wind Waker (GCN)
The art style of The Legend of Zelda: The Wind Waker would lend itself well to the HD capable Wii U. A port with Wii controls or the Wii U tablet would be wonderful all to itself. Imagine exploring the Great Sea, seeing islands with the game's massive draw distance, weathering impressive storms, and sailing from place to place via the King of Red Lions boat. The cel-shaded style of the game is already breathtaking, so putting it in high-definition only seems like the next step in making for a scrumptious package.
Super Mario Galaxy series (Wii)
Imagine traversing planets and planetoids alike in and HD version of the Super Mario Galaxy franchise, the Wii's most graphically competent game series yet. With the Wii U, fans could play through these games either with a dual retail release on one disc or through downloadable means. Whichever the way, Mario would never have looked so brilliant and vibrant. Nintendo has already made two of the best reviewed games this generation, so why not share them with the HD crowd? It makes too much sense to this superhero!
Ratchet & Clank series (PS2)
What is the hold up for a Ratchet & Clank HD collection? We've seen Kratos in HD, Ico and Shadow of the Colossus, soon to be Silent Hill and Metal Gear, so how about everyone's favorite lombax? With the addition of trophies, all four (or three depending on your view) classic Ratchet titles would simply look grand in HD and have oodles upon oodles of longevity and lasting life. Whether he's taking out Dr. Nefarious's half-baked plans or taking down Megacorp, Ratchet and Clank is one team you don't want to mess with!
Tatsunoko VS. Capcom: Ultimate All-Stars (Wii)
This Wii-exclusive fighter took the worlds of anime company Tatsunoko and game lords Capcom and shifted their worlds on their heads. The mechanics (in my opinion) outclass Marvel VS. Capcom 3 easily. It's just a more fun game with two-on-two teams as opposed to the triple threat teams of MvC3. Regardless, just picture the colorful cast and characters in brilliant and vivid high-definition graphics and online that works much better than it does on the Wii. It's a game that deserves to be played by as many people as possible, it's Tatsunoko VS. Capcom: Ultimate All-Stars.
Phoenix Wright: Ace Attorney (DS, WiiWare)
Hold it! We've seen Phoenix Wright in SD form enough already, so now it may be time for him to shine in heavenly high-definition. Objections and being out of order would never be so delicious to look at. The character models would stay in 2D and animate even more beautifully than they already do. All the courtroom drama on a giant well-formed screen would make for a brilliant-looking game-- more so than it already looks. With rumors (and a leaked character list) from Ultimate Marvel VS. Capcom 3, we won't have to wait long to see a 3D model of Phoenix Wright in HD.
That's but a small sample of some of the games I'd love to see in HD. What about you? There must be other games or trilogies that you'd love to see get the high-definition treatment. List any and all such titles in the comments section.