I didn't like it that much at first, but it's grown on me. The app we used before was such a POS though, that anything is better. It can get quite complicated though. We use it for Change Management and Problem Management as well as tickets, and have a lot of things setup as tasks.
One thing that really helped me after we first got it was to setup custom pages for my queues. The default view it came with blows, so I setup a page where I have my Tickets Assigned to me Unresolved, then My Groups Tickets - Unassigned, then My Resolved Tickets. Makes it pretty easy to see what I'm working on and what's in our queue in one quick view. I also have a few other pages setup so I can see other queues or see what tickets my co-workers have assigned.
One thing that's annoyed me so far is how difficult it has been to get certain changes implemented. It's probably something to do with the contract we have with them, and likely varies by your agreement, but it has taken forever to get some stuff done. Right now there is a bug that causes a ticket to auto refresh the page a few seconds after you enter it, which will wipe out any notes you've entered but not saved. We have multiple tickets to the devs for this, and it hasn't been addressed yet. Also we requested some features and fixes, and recently they were implemented. But this was stuff we requested over a year ago. Long enough that I can't even remember requesting them in the first place. Really annoying, but like I said that probably varies with how much $$$$$$ you're willing to pony up.
Tremendously expensive and not sure it is worth it unless you're a really big company. We got a new CIO at the last company I was at and he made everyone get ITIL Foundations certified (a waste) and sold the company a bill of goods on ServiceNow. This was for a department of like 20-30 IT people with 500 people in the company.
LOL, our now departed CIO also made everyone get ITIL Foundations certified and then implemented ServiceNow. Our last ticketing system was so bad though, ServiceNow is a vast improvement. I'm sure there is better out there. I used to like Remedy at a past company.