After all these years, and growing up with Windows 3.1, I have seen an entire evolution of computers and software. Touch screens and large resolutions were a pipe dream just 15 years ago. Now it's the norm. Going from a Packard Bell (yes, before HP) that couldn't run 3D Ultra Mini...
Don't stay in one place for too long if there are snipers about.
You can jump back towards walls you've already jumped off to avoid obstacles.
In the end-of-level scraps, take out anything with a gun before you deal with the others.