This game is much better than GTA: Vice City. The graphics are better, and shooting is better with the ability to manually aim. You also get to learn different fighting moves, so it's not always the same punch or kick. The map is also bigger than Vice City, with Las Venturas (which is basically Las Vegas) being the main area where I hang out. The missions are fun and the new characters you meet are great. You even meet someone from GTA 3.
Are you stuck on a mission? No problem. Play some pool at the local bar, play some arcade games at the 24/7, go to the gym and get yourself in shape, bet on horse racing, be a tourist and take some photos, or take your girlfriend on a couple of dates. If you have access to Las Venturas, you can go to the casino and gamble or go to the strip club. Do side missions as a cop or firefighter. The amount of things you can do is astounding. You can even buy clothes for your character's wardrobe. This is one of the best games out on the Xbox and should keep you busy until Xbox 360 or PS3 comes out.