I wouldn't say Coleman was a 'cheap' make, the general concensus on ukcs seems to be the Coleman is a good brand making quality products and well respected.
I would like to know that the HH is, but other than that seems a great tent for the money to me.
It is a shame it is 'pitch the inner first' as it is a bummer if it is raining, but tbh nearly all tents used to be made this way we are just a bit spoilt now.
Again re the door, yes the rain will come in, but the same can be said of our very expensive Outwell, as we choose to use the storm porch for storage! When camping getting a tad wet is not the end of the world.
Most of the negative reviews on Argos seem to be because they were faulty, 'pitted with holes' , not good in a tent , so I would want to pitch it before going away and give it a thorough check.
Have googled for you, it is actually a Coleman Canyon, must have been re-named for Argos, it has a HH of 2000, which is considered the minimum to be waterproof rather than showerproof. Here is some opinions of Coleman tents on ukcs, and here is some reviews of your (well the 8 berth but identical). The main complaint seems to be pitching, but that just takes practice, practice, practice.