None of those things would really be the T50s strengths. With some serious modding, perhaps you'd enjoy them for those purposes, but they tend to be pretty warm headphones, and a bit rolled off on the upper end.
The sound leaks a little, but I'd definitely say they are more closed than open. They are vented, which means some sound will escape. Now that mine are modded with some foam, they don't leak as much.
They are passable for gaming, though many dynamics have a wider soundstage which makes a huge difference for games. The detail is nice, though, so it's neither here nor there.
Your big problem is going to be for metal. People tend to like Grados for metal because they have plenty of mid-bass, have a really fast sound signature, and have that great aggressive high-end. The T50RP is a pretty warm headphone, which means it's a lot more lush than it is aggressive, especially stock. They have some bass, but not a ton of bass impact, the midrange is really detailed but warm, and the high end is relatively soft. This is pretty close to the opposite of what you want for metal, especially if what you're listening to is poorly recorded or compressed. The modding I've done on my pair have made them significantly brighter, which may help, but you could still do a lot better for that genre. They are good for folk and ambient, though. I see that you sold your MS1i, though. Why did you get rid of them, and what are you listening to now? We might be able to find something that will suit your needs and taste.
The other thing to consider is that they require a pretty beefy amp to sound their best.
