I have many complaints on WP but my 1520 doesn't have any smoothness/quickness/fluidity issues. The only lag/stuttering i see is when i try to move a tile from bottom to upper areas of the home but i also have something like 3 or 4 pages on it and the fact that some apps (including some of those you mentioned) take a long time to open but that's been like that forever not since now. I mean, i have mentioned other times that while i need my Android device to compensate for the shortcomings WP has in terms of OS and apps, my Galaxy Note II is almost unusable due to lag and lack of smoothness etc.. WP for me is extremely smooth. In that area is the best experience i had ever. Maybe a hard reset may solve your issues, in part?