Koh Samui, like Koh Phangan, is a large island. The taxi services run a monopoly on the island, like Koh Phangan. This island is a little less party and more tourist and family market. There are clubs and bars but is not as wild. This island is little more pricey compared to its two sister islands (Phangan & Tao). The beach is beautiful and plenty of activities on the island. Kick boxing events are a popular venue, as much of Thailand.
I stand in a hostel room, that I never got the name, above a tailor shop. The room was about 6 USD a night, from what I know, that is consider cheap on the island. Plenty of good food around the island but most of it is not cheap.
One could skip the island but if you do plan on going to Samui, I suggest two nights would be enough.