Personally, I really liked the gameplay in Mario Tennies Aces, it was just a little lacking in modes and features. Fever appears to address that somewhat, although it looks like it has less online features than Aces does. In particular, you can't play 2-player doubles over matchmaking like you could in Aces, only in custom lobbies, which look pretty barren from what I saw. I may still pick up the game at some point in the future for a discount, but hopefully they have some updates planned for the game and will add 2-player doubles to matchmaking.