Slide Five is the latest clone. The first successful clone was 2048, whose rules are a bit different. I got up to 1024 after playing it 4 or 5 times. I'm sticking to Threes!
I will say this, the graphics on Slide Five are faster and they're pretty slick.
Slide Five sticks pretty closely to the rules of Threes! The differences are pretty obvious based on the images.
Here's where I'm stuck at Threes! and Slide Five: what's the highest new tile that will be given. I'm pretty sure that in Threes!, it's 1/8 of whatever your current high tile is. In Slide Five, there is no '+' hint that signals, you'll be getting something higher than a five.
I've said many times, if you like a game, go ahead and pay for the upgrade - at least as a reward for the time you've been entertained already. In Slide Five, the game is free and you can pay $.99 to remove the ads. In this case, spend $1.99 to the true authors of the original game - Threes!