How much do the rules of Starfinder differ from Pathfinder?
I played D&D 3rd since its inception, and 3.5, and have been playing Pathfinder for some years now; so I'm very familiar with the 3.5 d20 scenario.
Is Starfinder still based in that or is it something entirely different?
Still based, but there's enough different to throw off the average player. Examples: No crit confirmation, 5-foot step is a specific move action and thus cannot be done if you don't move on your turn, full attacks are only 2 attacks at -4 instead of iterative.
I'd describe it as a little simpler? Again though, enough different the full rulebook needs a read.
Right on. So long as it doesn't fall too far from the tree :)
Some threads that discuss the differences
A staff blog post about differences
Small but interesting differences
New Starfinder Rules for Pahtfinder Players
A long thread about the differences (400+ posts)
And one of my early faves
Rule Differences Between Starfinder And Pathfinder
A pathfinderism i found out about today
When you use a reroll in starfinder you're not stuck with the reroll if its worse than the original