NOTE: I am not talking about the Guyver manga. I've never read it, I don't intend to.
Guyver is not very good. After finishing Votoms (a very good show), the highly legal website I was watching it on recommended Guyver to me. I thought it was live-action tokusatsu from the thumbnail, but it turned out to be an OVA (specifically, the OVA from 1989 to 1992, which is 12 episodes long). It was not very good, but in a kind of interesting way.
After watching and being generally unimpressed by the OVA, I decided to torture myself and watch the American live-action movies. I am VERY critical of American tokusatsu. From my experience they're ashamed to even be associated with their origins, and because of that go for a younger audience and have a wink-nudge sense of humour that screams 'I'm embarrassed to exist, so we can all agree this is dumb baby stuff, yeah?'. That, or they majorly overcorrect and become bland overly-gritty snorefests. The new American Godzilla movies are a sign that things might be changing a bit, but they've completely wiped out the practical effects aspect, so it's only tokusatsu by association. The Guyver and Guyver: Dark Hero did not raise my opinion of American toku.
Poor Mark Hamill. He's acting his heart out in this movie and for nothing - it's garbage. It's very clearly trying to go for the TMNT or Power Rangers crowd, so goes for grossout humour, straight up racism, and the most basic of basic plots. You can see some aspects of the original Guyver plot, but it has been so sanded down that you're left with a movie that wants to be anything else except what it actually is. Tokusatsu or martial arts fans will also be let down, as the suit acting is well below par. The Guyver is now an aikido aficionado, which mostly means he has a really silly pose when fighting. The Zoanoids aren't much better - it's all just boring, fights included. Seeing Mark Hamill turn into a cockroach was pretty funny, though.
The sequel is better than the first movie, but not by much.
In the end, Guyver is just not a very good franchise (manga excluded, I'm sure it's fine). I almost feel bad for it. There are so few American tokusatsu shows or movies that aren't just mutilated versions of Japanese shows. If you want to watch a movie about a hero fighting a biomechanical monster for the fate of humanity that includes humour and cool fights, watch Zeiram.