Even if this collection included only Sonic 1, 2, and 3, it would be worth it. As it stands, SMC+ just plain rocks.
The first thing you'll notice about SMC+ is the huge amount of stuff in this game. There are ROM images of 20 different games (although many of them must be unlocked through various painstaking processes. The one most worth the pain is the excellent Sonic 3 & Knuckles, which is the equivalent of attaching the Sonic & Knuckles cartridge to the Sonic 3 one and putting it in your Genesis for one huge game with all-new features. It requires loading Sonic 2 and Sonic 3 20 times each. Not playing, just loading. Believe me, it's worth the annoyance.), as well as hundreds of comic book cover scans, artwork, and a couple of game trailers. All in all, it's a massive package that will keep you entertained for a long time.
The gameplay of the original Genesis titles (except Sonic 1 to a limited degree) cannot be faulted. Threy are just a blast to play, despite the odd cheap trick (you WILL die several times from spike traps that seemingly appear out of nowhere). Sonic 3 & Knuckles is definitely the best, although Sonic 2 is also very good. The games are, true to their reputation, extremely fast. The graphics are also beautiful, with detailed environments and colorful sprites that seem almost too colorful for 256 colors. Sega has gotten a lot of mileage out of palettes. The four-button PS2 controller is a surprisingly good substitute for the six-button Genesis controller, and the default control scheme is intuitive and easy to use.
Unfortunately, many of the other games aren't so wonderful. The Game Gear games play like pale 8-bit imitations of the Genesis games with awful resolution, ear-wrecking sound, and jerky controls (partly because they are). Sonic Drift is a horrible racing game whose flat scenery, pop-up, and flickering make it look like some fifteenth-rate version of Wacky Wheels, which itself is a third-rate DOS PC version of Nintendo kart racing games. Sonic 3D Blast and its bastard Game Gear child Sonic Labyrinth are ugly isometric "3D" games with dull gameplay and no trace of the trademark Sonic speed. It's hard to pick a worst among the stinker games, but Sonic Drift is probably the winner. The omission of Sonic CD in favor of games like these seems criminal.
Every game looks and plays exactly like the original, right down to occasional glitches and slowdowns. While these are rare, one wonders if Sega could've ironed out a few bugs and taken more advantage of the PS2's hardware, which is orders of magnitude more powerful than the Genesis. Another point of contention is the emulator's savestate system, which is practically cheating, since you can save your game anywhere, even in the middle of boss battles (hint, hint for anyone having too much trouble beating a boss.) and the savestates take a whopping 260k of memory apiece. The original Sonic games can actually be quite hard at places if you're man enough (hedgehog enough?) not to (ab)use the savestates, but it's hard to resist the temptation.
SMC+ also comes with development artwork, 3D renders, and scans of the covers of about 150 issues of the mediocre Sonic Archie comic series. It also comes with the entirety of a special issue that recaps the beginning of the comic story arc. The issue seems poorly chosen, especially since scans of the later comic covers show a much better art style than in the beginning. Additional extras include two cutscenes from Sonic Heroes, which are interesting for a few minutes (although the pop-rock soundtrack must die.
Even if this collection included only Sonic 1, 2, and 3, it would be worth it. As it stands, SMC+ just plain rocks. There are some things that could've been improved and others that could have just been thrown out and replaced, but all things considered, SMC+ is well worth the money and highly recommended to anyone remotely interested in platformer games, classic games, or Sonic.
What's Hot: All the old Genesis titles completely unmolested, great value, generous selectiuon of extras
What's Not: All the really bad titles thrown in as well, the original glitches and framerate slowdowns are faithfully preserved by the emulator, no Sonic CD, saving anywhere takes away a bit of the challenge.
Also try: Sonic Gems Collection, Sonic Advance series, Super Mario Advance (GBA), Jazz Jackrabbit (PC)