I'm not sure what you mean by "powerfull", but I tracked every aspect of my family's financial life in Gnucash for two years. It had some issues with polish and usability, but it did the job.
Howeverf, I recently discovered Moneydance, and I love it. It's not free, but it's worth a lot more than they charge for it. [note: In my opinion, if you really want linux to remain viable you have to support the people writing usable applications]. The interface is clean and intuitive, and the feature set seems fairly robust (far more than I need, anyway)
There is a free trial...I highly recommend giving it a shot.