The long-time "missing" features have been for things like packet editing, scrubbing, and replay. As OS X has gained popularity a lot of people have asked for a native Mac interface.
Wireshark has one intrinsic "hard" problem. As networks get faster and resources expand people naturally want to open larger and larger capture files. We've made improvements in this area over time but Wireshark's job is to show you every last detail of every packet. If you have millions of packets that's going to use a lot of processing power and memory. You can alleviate the problem in Wireshark using capture filters and multiple capture files. CACE Pilot is a commercial solution that works with Wireshark and lets you drill down and isolate the traffic you're looking for.