It entirely depends on what you are after. It can do a great number of things thanks to it's Linux heritage (a non-bastardized linux like android) - and is very highly customizable thanks to that. So if you're looking for something with full Flash support, has a growing number of apps, and works more like a computer than a phone.. then it's excellent.

If you want an iPhone that's not an iPhone - you probably need to looking at androids.