If you've played past entries in this series, you're likely familiar by now with how things work. To recap, there are eight robot master stages that you may attempt in any order you like. Once those are out of the way, you'll battle through Dr. Cossack's castle. When that's done, you find once again that your nemesis is Dr. Wily. If that came as a shock to you, well, you're new to the franchise.
As did Mega Man 3, this newer title introduces new companions and gameplay elements. You can now power up your arm cannon. This is called the Mega Buster. Powered up shots will do more damage to your opponents, be they robot masters or even common toadies. Therefore, you'll want to spend any 'running' time powering up your arm cannon while you're on the go, just so surprised enemies can receive a powerful blast in greeting.
Also, you have a new companion named Fliptop. He comes upon you at set locations and will toss random power-ups your way. It's always worth finding him to see what he holds for you. Basically, he replaces the item canisters found in Mega Man 3.
Good on the basics, then? Glad to hear it. Let's get moving.