I took Escitalopram for approx five years. I found it was helpful for reducing my anxiety and it put an end to my intense and frequent anxiety attacks, making them a rarer and milder experience.
As for putting on weight...I am unsure whether this is a certain side-effect. My life-style changed dramatically during the time I was taking Escitalopram, for reasons unrelated to the medication. I moved away from my parents, I drank alcohol, I ate processed and fatty foods and I got less excercise. Before my life-style became unhealthy, I did not put on weight. Once my life-style became unhealthy, I did put on a lot of weight and continued to do so until I made healthier choices.
That's just my experience. Based purely on my own experience, I would say that healthy food and excerise will do more to keep you a healthy weight than what medicine you take. These healthier choices were difficult to do while depressed, but when I could manage to do them regularly again, they were a great (albeit gradual) anti-depressant in themselves.
Of course, have a word with your GP (or the appropriate medical person) if you're worried about what you're taking.