Some people would say Mario Tennis is worthy of praise solely for the fact it introduces the glorious specimen known as Waluigi into the Nintendo World. These people are right, but you can't write a full review out of that.
In all seriousness, Mario Tennis marks a highlight in Nintendo's adaptation of the sport into a fun, casual style. Tennis on Wii Sports arguably had the greatest impact across populations, but Camelot's N64 entry made tennis a "Nintendo thing" much earlier.
Accessibility is high when it comes to hitting the courts. Anyone can pick up a match just by moving around with the control stick and hitting either the B button for a slice or A for topspin. Once that becomes second nature, A and B can be combined and charged to execute more technical shots. The position of the ball when it's hit as well as the direction the player is moving during the strike also have an effect on power and placement, so there are plenty of elements to manipulate without being overly complicated.
Good old traditional tennis matches offer a variety of options for up to four players; you can choose from singles and doubles play on a selection of court surfaces that influence ball bounce and speed. The "normal" choices such as grass and clay are present, but there are also courts with character portraits that will change up ball conditions in ways you might not get out of real life. Both exhibitions and tournaments can be set up with the ability to control numbers of games and sets needed to win matches (and if none of these tennis terms are making sense to you, don't worry - the original game manual does a great job explaining everything).
Want to play something more unorthodox? Mario Tennis naturally has you covered. The Bowser Stage is the wackiest, throwing a dash of Mario Kart in with item blocks that can aid players or hinder opponents; the entire court is also suspended over a lava pit, making it tilt depending on players' positions. it's an uproarious party-style mode for those who aren't too serious about scoring.
Ring Shot adds target rings to centre court, with points scored for hitting the ball through them. These points are then scored by whoever wins that tennis point, often regardless of who cleared the rings. This of course places greater emphasis on ball control, and there are four sub-modes that add further focus on time or number of balls. Doubles matches can be played in this mode, with teammates either working together or jostling each other about chaotically in a free-for-all, scoring individually.
Piranha Challenge is a single-player mode that has three ball machine-like Piranha Plants spitting 50 balls from opposite court. Not only must these balls be returned, but there's also a computer player on the other side who will try to blast any return shots back at you! It's a tough mode, but a good way to learn precision and outplaying an opponent.
All modes, traditional or non, can be taken on with a well-sized roster of 16 characters, two of which have to be unlocked. Players can excel at speed, power, technique, or tricky shots, or they can be all-around Joes such as Mario or Luigi. Waluigi's presence has already been announced, but Mario Tennis is also the first time Daisy could be chosen as a playable character. Birdo's in here too, which is nice as this particular character isn't always a choice in multiplayer titles.
What isn't here, unfortunately, is all the material that could be unlocked in the original N64 title by connecting it to Mario Tennis for the Game Boy Color. This includes the four original characters from that title as well as extra courts that added more combinations of ball conditions. All of these extras were also inaccessible in the Wii Virtual Console version of the game. It also could have been fun to have had a story mode of some sort, as Camelot has proved it's good at making silly little scenes with Mario and company.
For going on 15 years old, Mario Tennis still looks good. The character models are a bit jagged, as was common on the N64, and not everyone looks up-to-date, but everything is bright, colourful, and animates well with no slowdown. The music is Camelot's familiar "ambitious" style, and gets pumping even more on crucial points.
Mario Tennis is a fun, upstanding game that can still be worth playing today; there's little argument in that. It has to be noted that an all new entry in the series, Mario Tennis: Ultra Smash, looms on the horizon, though. Those who want to see if the newcomer offers more might want to wait until its release before taking up a predecessor. On the other hand, those who just want some uncluttered, entertaining, easy-to-dive-into tennis for when folks come over should have much fewer reservations on serving this game up now.