Good browser games like RuneScape are hard to come across, the game is definitely a leader in the space and not much stands up against it. I've put together a short list of alternative online games that will please anyone searching for their next browser MMO.
I've had a long history with the RuneScape game (I held a free RS membership for a long time), playing the game on and off since it's early days. I would keep going back because I always loved the accessibility that a browser based game provided. I think it's a great genre and now with faster internet speeds and better technology browser games are just as good as their downloadable counterparts.
I'd love to hear from other RuneScape or browser MMO fans in the comments so don't hesitate to leave a message.