Just as good as when it was first released.
The general premise of the game is a lot like the Contras of yore: you blow stuff up. There's a meagre attempt at a story within the game, but it could really be completely ignored or omitted without much downside. The real meat of this game has always been just blowing everything up and having a blast (no pun intended) while doing so.
One of the best features of the game is the inclusion of a "hit" system that other later Star Fox games have been sorely lacking. In brief, you get one "hit" for killing a minor enemy. If you charge your laser and then take out multiple enemies, you get double the hits for each enemy killed after the first one (for example, killing five enemies with one shot nets you an extra +4 Hit). You also receive bonus hits for taking out especially tough enemies, and a +10 Hit for taking out bosses.
Each level gives you a hit counter where you can see how many you've gotten for that level. You'll also get a medal on each level where you get an exceptionally large number of hits. In addition to that, there is a high score list that keeps track of the largest total numbers of hits accumulated through one play-through of the game.
All of this works beautifully in turning the game into a simple bout of fun into some serious gameplay. No longer do you simply try to beat levels. You try to brutally and mercilessly destroy levels by amassing the biggest, baddest hit count you can possibly get. It sends the replay value of the game through the roof.
For only $10, this game is a blast that is easily worth every penny. It should be an addition to every player's Virtual Console collection. If you haven't already bought it, go do so right now.