It suffers from a few bugs and aging issues, but certain parts of the adventure make it all worthwhile.
Story - 8.0
The plot is split up into six different stories, each of which are told by the playable characters. The story for each character all relate to the same plot and are all told from different perspectives, but they all eventually lead up to the same, semi-epic conclusion. The story isn't bad, and there are certain times where the story can actually be a tad bit interesting to follow depending on which character. Some of the characters can be rather boring to follow, however (*coughBigTheCatcoughcough*).
Graphics - 7.0
The graphics were most certainly not up to par with the GameCube's capabilities, but do bear in mind that this was a Dreamcast game. The graphics are somewhat pleasing to the eye despite the glossy character make-overs, and they generally look pretty good, even if they do show their age.
Sound - 7.5
The soundtrack has some pretty good tunes, but some of the songs can also be very annoying (*coughMySweetPassion*). The soundtrack isn't overly memorable overall, but there are certain songs like "Open Your Heart" that seem to make up for some of the not-so-good songs.
Gameplay - 7.5
Due to the fact that there are six playable characters, the gameplay varies quite a bit, and that's where the game's major problems come from. Sonic's levels are the best parts of the game and are very fast-paced and are examples of how Sonic should be. Tails's stages aren't as good as Sonic's, but still pretty good; the main objectives in his levels are to beat Sonic to the finish by flying across shortcuts and other such things, and they're usually quite fun.
Knuckles's stages are generally the most frowned-upon stages of the Sonic Adventure games. The objective of these stages are to collect three pieces of the master emerald, and it can get tedious after a while, but luckily they aren't as bad as they are in Sonic Adventure 2 and are actually tolerable in this game because they don't take forever to complete.
Gamma's stages are.... okay. They aren't bad, but they're not great either. They are somewhat enjoyable though and are actually better than Knuckles's stages. Amy's stages aren't terrible, but the problem with her stages is that they are a bit too slow for comfort. The objective of her levels are to escape from each level so she doesn't get molested, er I mean kidnapped by the giant robot that's trying to take her back to Eggman for his own evil deeds (he's a lonely man you know...). Amy's levels are painfully slow, and it's annoying to have to constantly deal with the robot that's trying to hunt her down, but if you're willing to overcome that, Amy's stages can be slightly fun because of the platforming elements.
That now brings us to Big The Cat... The main objective of his levels is to catch Froggie... by fishing. Big is very fat, very slow, and very annoying. Once you catch Froggie at the end of each level, Froggie runs away (who wouldn't blame him?) and Big is forced to find him yet again. Fishing is just as boring as it sounds, and it's by far the worst part of the game.
Aside from the levels, there are hubworlds in which you go through in order to access levels and sometimes cutscenes. The hubworlds mostly consist of pointless fluff that should've been done away with, but luckily most of your time is spend in the levels and not in the hubworlds (unless if you prefer to explore said hubworlds).
Most of the game design doesn't hold up so well by today's standards because a lot of the levels you play through (except for Sonic's and Tails's) feel dated and not as fun as most people thought they were back in 1999. Sonic's and Tails's levels still hold up fairly well, however, and their levels make the adventure all worthwhile. It's not that the other characters are terrible to play is by any means (save for Big the Cat), but their levels aren't nearly as good as Sonic's and Tails's stages.
Difficulty-wise, the Sonic Adventure is actually on the easy side, unfortunately, and the only challenging parts of the game are Sonic's levels.
Verdict - 7.5
Overall Sonic Adventure has aged rather poorly in certain parts of the game, but some parts like Sonic's stages still hold up well and enduring the collecting, shooting, sluggishness, and fishing all feel worthwhile once you unlock the true final story.
Overall:
If you never got to play Sonic Adventure on the Dreamcast then this buggy port is worth playing through at least once. I paid $10 for my used copy, and I'd say as long as you get it around that price, then it's most definitely worth a purchase. If you find a copy that costs more than that, then you're getting ripped off. If you would rather play it in HD, then it's also available on the XBLA and PSN.
The Good:
- Sonic's stages
- Tails's Stages
- The storyline isn't bad
The Bad:
- Big The Cat's stages
- Sonic's levels are the only challenging parts in the game
- A few bothersome glitches, including camera issues