Some years ago, it was hard to compare this low-cost airline with its grown-up competitors. Not anymore. At least on some key routes, Wizz Air is clobbering its competitors.
For a trip to Brussels, especially if it's a short stay, Wizz Air is the choice. At half or even a quarter of the price you pay some of its air transporters on this route, Wizz Air is all simple and casual. You are told about that and it works. They were punctual (in fact, they had an average of ten-minute delay at departure, but sped up and landed on time).
You know you have to pay for the food and, in fact, the no-fancy sandwich purchased on the Wizz Air plane is totally ok, much better than the stale pizzas and brackish sandwiches they shamelessly sell on the Charleroi airport; and you pay a fair price for it in the plane, like you're in next-door fast-food in your neighbourhood.
Definitely it's worth the 30 euros or something you pay for a flight with them (one way). Even with the cost of the train from Brussels to the Charleroi airport (somewhere at around 16 euros), Wizz Air is a better option than the fancy pancy Brussels Airlines where you are charged hundreds of euros just because they land you one-hour closer.
Now: the proximity and quality of the airport is a problem. To reach Charleroi from Brussels is not really a problem. You get lots of trains taking it you to the Charleroi South train station. From there, you have to take a bus for another 20-min ride.
Distance might not be a problem if you don't mind one hour or so from Brussels. But Charleroi airport is a rundown hangar. You get in through some literally big, white tents and once you pass the security, you have basically not much choice to spend your time. Make sure you bring a good book because there is not much to do here. The few eateries seem to be competing in offering unappetising food. The toilets are disgraceful.
If competitors beat Wizz Air in price, the Charleroi airport might be the killer of this route for Wizz or other low-cost players. Until then though, it remains the option for many types of visitors to Brussels.