Phantasy Star IV is often considered one of the greatest games ever made for the Mega Drive. It pushes the system to its limit, with great graphics and sound, and a ton of content - You aren't going to finish this in a few days. RPG fans also consider it one of the best games of the genre - It could very well also be the best RPG currently on Virtual Console. Strangely enough, despite the game's greatness, it never got a sequel - Every Phantasy Star game that has followed since is not part of the main story.
Mega Man 3 doesn't really need any explaining - It's Mega Man! Most people consider this the only classic Mega Man game to give Mega Man 2 a run for its money, which is quite understandable - With 8 awesome new Robot Masters, another great soundtrack, good level design and two new gameplay elements (The slide and Rush), Mega Man 3 is everything Mega Man 2 was, plus more. Don't hesitate to download it if you liked the second game - You might find that you'll like it even more!
Just the two on VC this week - But both of them are terrific, so there's nothing to really complain about!