SMB is awesome, and there is no doubt about that. But how about having SMB on the go? That equals 2X the awesomeness. But, there have been bad console-to-handheld ports, so I'll see how this stacks up.

The graphics aren't improved from SMB. The graphics added in are good. None of the graphics are bad on the eyes, and almost all, if not all of the graphics are good.
+SMB graphics aren't a really bad thing
+Added graphics are well-made
+None of the graphics are ugly
-The GBC is capable of much prettier games
The sound isn't remade or remixed from SMB. Some songs are added in, and they sound decent. Just like the graphics, none of the added tracks are bad, and almost all of them, if not all are really good. Nintendo could've tried to remake the graphics/sound, but it probably wouldn't have turned out as well as it did.
+SMB music tracks are really good
+Added tracks are good
+Nothing sounds bad
The story is the same as SMB. Nothing new, nothing old. The Mushroom Kingdom was invaded by the Koopa tribe,(which is the only time they're referred to as a tribe) and their dark magic turned the residents of the Mushroom Kingdom into stones, bricks, and plants, and kidnapped the Princess, who is the only one that can undo the curse,(which is the only time they tried dark magic that I can think of that wasn't just to harm/kill) and the overall-clad plumber comes to the Mushroom Kingdom for no apparent reason other than he feels like it, and he finds out the Princess is in trouble. He decides to try to rescue the Princess for no apparent reason other than to be heroic, and that's it.
+Story began the Mario series/saga, and was not a really bad start.
The gameplay is classic SMB. Nearly flawless. However, the game received a new problem with the transfer to GBC: Screen size. There's no way they could've fit the entire level, top to down, on the screen at the same time, so you have to press Up or Down to scroll the screen in that direction. It's not a game-breaking problem, but it does get in the way.
Oh, but there's so much more than just SMB. There's a lot more in this package.
The game has normal SMB, 3 save files, and much, much, more. There's a new map screen, which is a decent graphical improvement, the ability to switch between Mario and Luigi on the map screen with the Select button, both quests, a clear list, most of the wacky but wonderful glitches of the original, a fortune-telling minigame, the ability to race a Boo in 8 different levels once you get a score of 100,000 or more on the high-score board, a photo album which expands as you do certain tasks, a Challenge mode that challenges you to collect 3 medals for every level in the game, a Vs. mode that lets you play with another person as long as you have a Link Cable, two GBCs,(or GBA, if you have that link cable, and your friend has one as well) and two copies of the game, the ability to transfer high score boards with the Link Cable, and then there is the feature that is the best added feature out of them all....*drumroll*

THE LOST LEVELS!
This game has the real SMB.2, in all its glory. Worlds A-D are cropped off, as well as the wind element from the game, but that doesn't mean that it's any less awesome. So, in total, this game has 96 levels to go through, counting SMB 1's second quest. Pretty good, considering that this is a GBC game.
+Enormous amounts of content, for a GBC game
+The Lost Levels
-The Lost Levels are missing some content
-Minor camera issues

So, let's recap.
PROS:
+SMB graphics aren't really a bad thing
+Added graphics are well-made
+Nothing is really shabby in the graphics department.
+SMB music tracks are really good
+Added music tracks are really good
+Nothing sounds bad at all
+Story began the Mario series/saga, and wasn't really a bad start.
+Enormous amounts of content, for a GBC game
+The Lost Levels

CONS:
-The GBC is capable of much prettier games.
-The Lost Levels are missing Worlds A-D, and missing the wind from some levels.
-Minor camera issues.

Is it worth playing?
Yeah. If you can get this game irl, than it will be a really awesome purchase. If you're not sure, then, by all means, play it on Vizzed! You're sure to like it, and if you don't, then that's fine by me. If you have a GBC and an NES, and you have a choice between this and the original SMB, pick this.

Overall Rating:Excellent