It suffers a bit from having been around a long time with a lot of development. It's architecture, especially in Salesforce, is sprawling and it can take a while to learn it. They are working to improve documentation, but it's not always easy to find what you need. Newbies are often a bit frustrated getting up to speed. The autoresponder setup in Salesforce suffers from this problem especially and the Connect receipting isn't quite ready for all my clients have needed it to do, but it is improving!
The ability to change the recurring amount or related Salesforce campaign without cancelling and restarting a subscription would be a massive improvement for how most nonprofits manage recurring donor programs. Of the 10 or so setups I have done in C&P, this is always a wish!
The newer Connect interface looks and operates *much* nicer than the portal but often is a bit clunky for doing a lot of data work (You can't click back in most windows, update a bunch of transactions at once, etc). If you can do most of it in Salesforce, you will be better off.
Several clients have had less than stellar response rates from Sales (getting accounts set up, quotes for importing recurring gifts, etc), which is surprising given how responsive the tech support can be.
Finally, I rarely use C&P Events in Salesforce because the setup and learning curve is really large for nonprofits. It suffers from being too powerful for most of them. Staff can't easily setup events without admin help and it isn't easy to customize the experience for things like free events or addon donations. It is pretty powerful though, just more than our clients have needed. Review collected by and hosted on G2.com.