A game is an entire package. Presentation, graphics, playability, and re-playability. I don't think anyone chooses a game for just one or two of those reasons. They all factor in a little, but I think the more successful games will have a solid gameplay first and foremost before adding the "fluff" of graphics and presentation. But the presentation and graphics do have a role to complete the whole experience and to entice people to play.
There are games that have an awesome presentation and graphics, but fail miserably in playability (Tribes Vengeance) and therefore ultimately fail as games. Then there are some that have great playability and re-playability with zero or poor graphics (Nethack or Minecraft) and are big successes. I still go back and play games from my childhood with limited graphics because the playability and re-playability is solid. I think the most important point is to have a presentation and graphics that compliment the gameplay. Games don't have to be fully 3D to be fun. Just look at Farmville or Mafia Wars.
