Seriously under-appreciated. (Notice a trend of people saying this?) Fun controls and gameplay.
I suspect that the readers who are giving this game high marks are the ones who actually know the genre. Now, Heatseeker is not realistic. It's not even close to it. Unlimited weapons, low operational ceilings, weapon behavior, radar, everything screams arcade. And that's OK. What Heatsekker does offer is a control scheme that is second-to-none. Flying is incredibly enjoyable and intuitive. Blowing bad guys out of the sky is rewarding and fun.
The professional reviewers love to harp on the game's graphical shortcomings, but in my opinion, the game looks fine. It's not a powerhouse like some PS3 games, that's true. But the simple reality is, the graphics look fine. You can see what you're doing, and understand what you're supposed to be looking at. And really, when the impact cam switches on and you watch your missile (unrealistically) slam into your target, you will get a rush of satisfaction. And that's really all that matters. I would much rather enjoy my games and put up with slightly outdated (but not ugly) graphics than hate the experience but have pretty shiny oh-so-real graphics. I don't know. Maybe Gamespot hires raccoons to do their reviews.
The bottom line is, the Wii needs more games like this. The flying just FEELS right. It's a fun and satisfying game in a genre that is too neglected, both by developers, and reviewers who have no idea what to do with these kinds of games.