1) Little Fighter 2 - LF2 is one of the best freeware fighting/adventure titles that I have played. The fighting in this game is similar to the combat in Super Smash Bros with lots of items to appearing during the battle. LF2 has many different characters to choose from and has a number of different gaming modes such as tournament mode, single fight mode, multiplayer mode, and a sort of adventure mode that is reminiscent of the Streets of Rage series for Sega genesis. You can find this game here.
2) Jetz Rampage 4: Revenge - Are you a fan of the Grand Theft Auto series? Have you played all of the games in the series and beaten them thoroughly? Well, then you probably won't be that impressed by the Jetz series but the gameplay is similar. As far as freeware titles go, this game stands out among the best. Released by the late freeware game-maker known online as Shawn64, Jetz 4 is a mission based action game where you control a jetpack wearing, gun toting robot. The object of the game is to speak to certain characters and receive fun missions such as picking up and dropping a certain amount of people and sniping targets. The game contains 2 huge (and quite populated) cities to play in as well as many weapons to choose from. In fact, you can even create your own weapons and import them into the game. The game is a bit violent so I can't really recommend it for young children. That being said, you can download this title and begin the mayhem here.
3)Sonic the Hedgehog: Time Attacked - Of all the Sonic the Hedgehog fangames (home-made games based on characters or gameplay of a professional game) out there, this one is the best hands down. Most other Sonic fangames are full of glitches and feel stiff in the sense that the movement engine of the game lacks physics such as acceleration and momentum. In other words when you move forward, you're instantly running at max speed and when you stop, you stop instantly. This is not the case with Sonic: Time Attacked. The gameplay is great; it really feels as if you're playing a genuine Sonic the Hedgehog game made by Sega. The graphics are very good as well, combining 2D and 3D models, with very impressively drawn cutscenes. The bottom line is that if you're a fan of the classic Sonic the Hedgehog games, you should download this game immediately. Find it here.
4) Operation Spacehog - Spacehog is a fairly simple side-scrolling space shooter game. The graphics are nothing fancy and the game's concept isn't original in the least since it's basically a Gradius clone but that doesn't stop it from being a lot of fun to play. You can choose from 1 of 3 ships, collect power-ups which increase your firepower or defensive capabilities, and play either single player mode or multi-player mode. That's about all there is to say about this game; Spacehog follows the stand side-scrolling shooter formula but it does so very well, especially for a freeware game. Download it here.
5) N - Yes, that really is the game's entire name. The fun of this game lies in it's simplicity. You control a small stick figure man through 500 levels where your goal is to collect yellow squares which will open the door to the next level when they are all collected. The catch is you must collect them before your time runs out. You are given a small increase in time for every square you collect. The graphics in this game are simplistic flash graphics that aren't anything special. The physics engine is what makes the game enjoyable. Your little stick man will bounce off walls, accelerate over time, run up curved walls, etc. You can even create and import your own levels. Download the game here and give it a try.