My wife and I booked the Gateway just a few days before our stay, as we were attending an event in Cardiff. It turned out to be a very good choice.
I'd rang in advance to see about early check-in, which was helpfully accommodated by the staff, and our room was just what we needed for one night. It was comfortable and clean, there was parking outside, and the breakfast the following morning hit the spot too.
It was no more than quarter of an hour on foot to Newport train station, all main road and into the centre, and we had no problems walking back after midnight.
Don't expect high-class luxury but if you just need a base for your stay before going off elsewhere, you won't go far wrong.