I've been on lamictal for 10 years, and have been seizure-free the whole time. I experienced bothersome side effects the first few months (very restless sleep/vivid nightmares) but those went away, and I haven't had any problems since. No cognitive or mood-related side effects as far as I can tell. In the past decade, I have also aged out of my 40s and into my 50s, so I would like to blame my grey hair, wrinkles, minor weight gain and changing vision on the Lamictal, but that may be a stretch.
I'm able to take the generic form (lamotrigine), so the medication is inexpensive -- about $30.00 for a 3-month supply.