Season 8, in my opinion, is a mixed bad in which the gems have been the best we've seen since season 4.
Most of the specials are better than meh. Frozen Face Off, Ghoul Fools, It's A SpongeBob Christmas!, and Hello Bikini Bottom! were all great. (I didn't see A Squarepants Family Vacation yet).
Sandy had more screentime. More plots focus on her and her traits are more or less starting to get diversified. What I really want from here on in is for her Texan side to return at full swing.
SpongeBob isn't as annoying or stalkerish as he was in seasons 6 and 7. He's becoming lovable again and regular again.
My only complaint is that Patrick is still stupider than stupid. I want him to make witty remarks like the old days again.
Season 8 reminds me of season 4 in which both seasons had good gems but were mixed bags.
Season 9 is a little bit meh. It's got great episodes like Eek! An Urchin and Plankton's Pet. I haven't seen some of them like Jailbreak yet. It reminds me of season 5.