If you familiarize yourself with the various additional fees Volaris has in place, you will eliminate most of the complaints I hear folks say of Y4. Most folks I hear complain, book the basic/cheapest fare on Volaris, and then are surprised and livid once they find out they have to pay for checked-baggage, or a bigger/heavier carry-on bag, or seat selection, or to change their itinerary. If you know beforehand that you'll require of any service that charges a fee it is cheaper to pay online/pre-flight than to do so at the airport counter fyi.
As for their planes they fly A319s A320s, and A321s. In an all economy setup. Some seats are better than others just like in any other airline. Seats do not recline (at least in aircraft I've flown). Clean and simple interiors. Bring your entertainment. But most Y4 flights are 1-4 hrs depending on route, so even the longer flights aren't all that uncomfortable in seat/cabin for duration.