I can only speak of the PAL version of the virtual console. It's got different - and fewer - games to the US and Japanese versions. There's an awful lot of rubbish on there, and a lot of "meh". There are some good games, though which and how many will depend upon your tastes. I can't recommend any NES games; not seen any which I wanted to download.

Paper Mario for the N64 is all kinds of awesomeness with a cherry on top. I loved it back in the day and I love it still. IMO it's better than both its sequels.

Zelda: Ocarina of Time is brilliant if you haven't played it before. Time has sadly dented some of its awe; Hyrule field is no longer jaw-dropping.

Super Metroid is available, the first time it has reappeared legally since its SNES release. It's widely regarded as a classic, and I wouldn't argue.

The various Sonic and Mario games are as good as they ever were, assuming you like platformers.

I used to love Ecco the Dolphin when I had my Mega Drive, spent countless hours on it. Nowadays I can't get along with the brutal difficulty. If hard games are your thing then Ecco is still the best game based around a dolphin.