Some the issues I had:
- WiFi connectivity
- Lag with Mission Control when invoking (on a retina Mac)
- Lag with animations in general
- Slow shutdown times
- Messages not syncing sometimes
- Mail is terrible
- Lag in Finder scrolling
- Lag with Preview documents
...the list goes on and on. I found it to be a terrible OS. El Cap, even in beta 1, vastly improves performance and fixes most of these issues.
I have the same system as you and had none of those issues except the messages sync bug which was an iMessage server issue unrelated to the OS. If the OS was such a huge failure there would be media reports. The media loves to report anything negative about apple.