"Frontlines" is a series of six books following the exploits
of Andrew Grayson from a naive teenager to a captain in the space army. Very
much in the same vein as "Starship Troopers" and
"The Forever War", with characters that you warm to, and
plausible bug-eyed aliens (they don't actually have
eyes), I liked it very much.
The series has been left open for a seventh book.