Another reviewer rates this as 'two' because Alien is much better than all of these films.
Quite right, Alien is much better, but competing with Alien is not what they set out to do! To judge it on this basis would be like saying that a Mini is no good as a car because it couldn't beat Lewis Hamilton's F1 vehicle in a race.
Instead, judge it against what it is: a TV series boxed set, and realise that what you're getting here are seven films by, gasp, 'masters of horror' for the price of one. Their combined budgets were probably less than that of Alien (or at least what Alien would cost today) and one of the commentaries mentions having just a handful of days to do all the shooting.
All are worth watching - I even liked the genuinely creepy Poe another reviewer rates as the weakest - and some are very good. I can also recommend the commentaries. (John, well done for not trying to kill your co-commentating script writers with your addiction, but if you can't go 30 minutes without leaving for a cigarette break, something's seriously wrong.)
The main reason for deducting a star is the absence of any subtitles. When the scripts are included (in PDF format for people with DVD readers on their PCs) there really is no excuse for this.