WagonR is a very good car in its segment (same segment as Santro). Today it's the most preferred car (alongwith Alto). It gives a mileage of 14/15 in city & around 18 on highway - depending upon driving condition & style. Maintainence cost is very low (like all Maruti cars) & service & repairs are easily available anywhere/ anytime. Features too are good enough - at par with Santro & so is its cost. It will meets with the general preference criteria of maintainence & support, perfomance, features & price tag.
Besides, WagonR being a tall car, it's more spacious (total space) & airy inside. The only weak point is that on high speed / highway at a speed of more than 90 or so, the road grip is not as good as Santro & the like, and is, therefore, like all tall cars, relatively more prone to high speed accidents.