I am on the fence. To me, it feels like they made it much more android like in appearance. I don't necessarily consider that a bad thing because I think the previous look was boring and most android phones I have played around with (never owned one) seem overly complex with layout. I am on the fence, as said, but the more I use it, the more I am used to it.
My battery seems to drain faster but I am checking a lot of stuff out.
One major problem I am having is WIFI. I will admit I don't have the best WIFI signal throughout my house but now I am getting "cannot connect to server" a whole bunch. Normally I would not attribute this to an OS upgrade but I test my wife's phone (same phone) and it works like my old did. It seems now if I have a week WIFI signal, it just doesn't work at all, rather than being a bit slow. I find myself turning off my wifi when in certain rooms.
I do like how I can easily add a lot of pictures to message and email. I know you can do that on the old iOS but I never did it much so it wasn't worth the time looking it up online and seeing how to do it, the few times I needed it. Now I find myself using the multiple picture function way more as it is actually intuitive now.
I don't find it slower but I do find I get short hang ups. Some are Apple apps, more are 3rd party apps.
I am likely not the best reviewer, I am not super into Apple stuff, to me it's just my phone. I feel like all issues will be resolved in updates anyway so I am not going backwards.
The best thing for me about the update is in some ways, I feel like I have a new phone, for good and for bad. I am sure that isn't something Apple wants to hear but it took my want to upgrade down quite a bit. Not that I would upgrade until my contract allows me but I won't be saving my pennies for the 5s (I have a 4s so even though people are disappointed with the 5s, I am not because it will be a good upgrade from the 4s). I may wait for the 6 even, not sure what that will be but I like the size of my 4s, the 5/5s is fine, I don't think the 6 will be smaller but it may bring the cost down.
I know that is semi off topic, just saying that the new iOS is intriguing enough with the new look to make me feel like I just bought a new phone so I am content with just something new, as said, with the good and the bad.