Why this wasn't as good as the original...
1.) They waited 20 years before actually making this, which is ridiculous on a lot of levels. Then you have to hear people saying over and over "20 years ago, 20 years ago, 20 years ago," and I'm like "I KNOW the aliens invaded 20 years ago! What has happened since then, you idiots?!"
2.) They act like almost nothing happened in that 20 year gap besides having slightly better tech that was reverse-engineered from all the ships that crashed to earth in the previous movie. You would think something like this would have happened at least 1-5 years after the first film, not 20.
3.) Will Smith didn't come back, so that left a huge hole in the film. Steven Hiller was an awesome character in the last one, and not to have him there, with an uninteresting adult son to fill his shoes was a very weak spot in the film.
4.) All the people we'd grown to love and cheer for in the previous film have either become old, obscure, or just plain unrecognizable in this film. I didn't even recognize Jasmine or the former president. And their presentations were very forgettable. It was like watching "The Force Awakens" all over again and seeing your favorite characters as old and faded. Not fun and causes audience apathy.
5.) The new ship, while obviously terrifying in both size and destruction factor (how often do you see a ship so huge it has its own gravitational field?) was not really all that exciting when it came to the devastation it wreaked on earth when it showed up. In fact, you look at what it does and think "Oh gee, like I haven't seen aliens rip up all the major cities of the world before. *snore* Wake me when it's over."
6.) Having Dr. Okin miraculously survive having his mind reamed and an alien tentacle STRANGLE him, as well as the president finding that he truly was dead, was ridiculous. They made it very clear that Dr. Okin was as dead as a door-nail in the first film after the alien was shot to death. Having him just miraculously come back because he was in a coma for 20 years is a common and over-used cliche from comic books.
7.) Almost nobody from the new generation were all that interesting as characters. They were extremely forgettable. I can't even recall their names right now.
I could go on, but you get the picture.