Overall, for a season that started out very slow and repetitive but redeemed itself several times, this is a well done conclusion to a rocky inconsistent, but overall good season.
The ending takes the series in an interesting turn because it addresses two underlying fundamentals parts of the series that were not addressed before.
1. The absence of Leonard
Some people think the main character of the series is Sheldon, since he is the most acclaimed and familiar, however Leonard is the main character of the series while Sheldon is often the comic relief. The premise of the whole series is the relationship between Leonard and Penny which will take another twist. But also, this will allow Sheldon to develop as a character, as he has been so reliant on Leonard for the entire 6 years. Of course, he has Amy to lean on, but this can also open up a closer interaction between Sheldon and Penny. Leonard was always the one to let the two completely different character reconcile, as he represented the middle-ground between the two, both nerdy and social. Now Sheldon and Penny will develop without Leonard's intervention.
2. The development of Raj
After the other main characters (Leonard, Sheldon and Howard) have all found relationships, Raj was cast aside as a secondary character where his inclusion wasn't as necessary for the series once Howard was married, ending the bromance. The writers saved Raj, the most enigmatic until now, for last but they inevitably had to address him.
Every season needs a bang at the end, a memorable moment, and in this one it was Raj overcoming his selective mutism and being able to talk to women. The writers slowly toyed with this idea by letting him talk only while he is (or thinks he is) intoxicated, but eventually, it was time to stop milking it and let it go. It was the right time to develop Raj in this way. It is suprising, but organic as well.
Lucy deciding to end the relationship with Raj is the last, and most important point I want to touch on and it has to do with the central idea the writers were aiming for. In the beginning of the series, it was presented that Leonard was a socially awkward nerd and Penny was the hot neighbor. The premise was the Leonard would be lucky to have a chance with her and Penny would have to date down (considering she had much more attractive boyfriends before Leonard). Now the two are established as equals, after 6 years, and the tables have been turned around a bit because now it is Leonard that seems very interesting while Penny is the more shallow one.
Raj and Lucy are a direct parallel to this. Raj asked Lucy out on the premise that he was alone and desperate and never would find a girlfriend. While Raj was rude, obnoxious and often times oblivious, it was Lucy as a whole that was flaky, socially dysfunctional and beneath Raj. While at surface value, Raj was the desperate one and he got dumped, looking deeper, it was Raj who developed a lot as a character (encapsulated by the end scene) to the point where he can do much better than Lucy.