The last time I posted on this thread was a year ago. At that time, everything was going well on generic levetiracetam. Since then, I have had the manufacturer change about four times. (This is due to changing pharmacies and each of those pharmacies changing manufacturers once.) Here's my experience:
Each time I switched I went through a period of kepprage, headaches, and other side effects similar to when I first started taking levetiracetam (though not as severe or long-lasting.) I might be inclined to chalk that up to psychological factors - just expecting symptoms, so getting symptoms.
However, I just had the manufacturer changed on me in November to one that I had never had. The side effects were awful. I had a headache almost 24x7, frequent bouts of kepprage, an eye twitch that was nearly incessant for a month, and some concentration problems (possibly just due to the other symptoms). What's more, while I was up to about 4-6 weeks between seizures, under the new manufacturer seizures increased in frequency until I was having them every few days (which is about what I experience without meds).
So, of course, I spoke with my doctor. We got back on levetiracetam from another manufacturer (one I had taken previously). This was about a week ago. Within a couple of days, the headache was gone, the eye twitch is only occasional now, kepprage is infrequent and milder than it has been, and I haven't had a seizure in a week.
This is just anecdotal, and your mileage will vary. But, I can say pretty conclusively that all generics are not created equally. I don't know that any one is better than any other, but I do know that at least one effects me very differently from at least one other.
As far as the overall effectiveness of generic vs. Keppra, I don't know that there is any strong evidence. There are stacks of people that do well on one and not the other. I think it really comes down to the fact that there is variability between manufacturers, and that UCB (the maker of Keppra) is just one of them.
-B