Mesmers are very complex and will take time to understand well. It is very unique in its approach.
When I played it, I was specifically testing its viability as a summoner vs traditional mesmer. Admittedly, I don't have a lot of experience with traditional mesmers, most of my shutdown career has been on a ranger. I did play mesmer in GW1 in both PvP and PvE, but I tended to stick to a few builds that worked better with my skills.
I really liked the GW2 mesmer, but it's clear that I have much to learn about them. I'd like to know how others play the mesmer in both PvE and PvP so we can learn about them together.