If you want good PVP in a 2D sidescroller, there are tons of better game choices than Maple Story anyway.
Think about it, games that were designed around having PVP from the start will always have better PVP than games that try to patch it in somehow later on.
WonderKing and LaTale would be my top suggestions if you want full 2D. If you are from EU WonderKing is the better choice and if you are from NA LaTale is the better choice.
If it doesn't need to be fully 2D, Dragonica has even better PVP.
It's not so much I was I need it to be fully 2d I was just in the mood for something different. Damn advertising got me as the Maplestory ad at the top of the forums got me LOL.
I agree with games that focus on pvp vs patching them in. I'll check out dragonica's review and LaTale. It wasn't a issue of about where I'm from (NA btw) but it seemed that Maplestory wasn't going to work with Windows 7.