I couldn't decide whether it was his best performance as Loki but I'm glad to see you've made your choice. Tom Hiddleston was I agree, really engrossed in his playing of Loki, as he had previously, but moreso in this instalment. Some of the scenes, especially with Frigga in his cell and when Thor finally comes to visit him, are very emotional and deep. Despite all that he says to Frigga about his birth and her role as his mother, I think the love he bears for her is clear to see and it is further shown when Thor comes to visit him and immediately calls his bluff of illusion.
Besides Loki, I'd also like to note on Chris Hemsworth's performance. It's really enjoyable when you can notice a character's personal growth through several films. The impact that the New York incident and Jane have on him, makes him almost unable to enjoy any time with his comrades or his victories across the many realms he's saved. Beyond the fights and action, I enjoyed those 2 character's personal, emotional scenes most.
You're right, Odin is a jerk. Even I went "ouch" after that scene; it was so uncalled for. Also when he instructs the medical team to stop examining Jane and have her returned to Midgard. Right that he could've been in that her place wasn't among Asgardians, but there are ways and times to handle such matters. Also his willingness to sacrifice the entire army in order to fend off the enemy's attack, instead of listen to Thor's plan of luring them away from the realm.
The ending was surprising. I thought something was quite suspicious when the soldier appeared before Odin in the throne room to report to him( note, that this is also the same soldier Loki disguises himself as when Thor breaks him out of the prison

), but I didn't really think much of it until the end. It was quite surprising. I'm not sure nor recall reading anything about the next Thor film but if the ending means anything, it would possibly be more focused on Asgard and the aftermath of Frigga's death and possibly discovering that Loki is on the throne. Where do you suppose Odin is now? dead? locked up somewhere?