From what I know of it, it's a bit like よ. However, while よ kinda emphasizes the fact that you're telling someone about something (you're giving them a piece of information), わ emphasizes the statement itself. In more extreme cases it sounds a bit like saying "
fuck it, I'm going to sleep", or "
that's it for me, I'm going to sleep" to me, though it's not nearly as strong as either of those expressions. It's not aggressive
per se.
At any rate, it has a slightly more manly vibe to it than something like よ, if that makes any sense. Which is kinda tricky by the way, because there's another わ that you'll hear much more often at the end of sentences, but that one is reserved for women. It very much sounds feminine, and it can even be combined with よ or ね　>> わよ / わ. I can't remember if you can even say わよね though.
In anime or games, while you will often hear men say 行くぞ" or 行くぜ as a stronger, more colloquial, more manly way of saying 行くよ, women will most likely say 行くわよ instead, because that's the strongest form of emphasis a woman can use while retaining this sense of femininity (ah, Japan and gender roles...). But that helps demonstrate my point that the わ I used is different from either this わ or よ.
TL;DR: Men's わ is roughly equivalent to よ, but the emphasis is put on the action rather than the listener/the fact that you're saying this to someone, so it's not a complete synonym of よ, and it's less commonly used. AND it's different from women's わ.
