Starting a fight, in an interesting way.
The first thing that jumps to view in this game is most probably the visuals. Everything looks fresh. Everything looks real and has a different feel, even though you can't really touch it. If you look up to the sky, you can see a moon or a star filled night. Look out into the distance and there are many things to enjoy such as a natural landscape or a destroyed city. It's interesting to see what little details you can find and how detailed the environment is, not to mention the effort that went into creating it. But, while looking at the game one can also find some frame rate drops and some texture mishaps, but all in all this is one of the best-looking games to date.
After (or maybe before) looking at the vibrant environments you start to notice the HUD. It's changed, that's true. You now have an actual health bar below the shield. This drops if you take damage while you have no shield. This makes you feel more vulnerable but also teaches you to be careful and that you can die easily, besides reminding you that regenerating shield doesn't mean infinite life. You die. Easily. Especially in the harder difficulties, but dying in this game actually makes you want to try harder and see if you can do better.
With the addition of new weapons such as the needle rifle, and slight modifications to old favorites such as the DMR, gameplay is more varied. You also have armor equipment, which if used correctly, can greatly enhance your chances of survival. You are also reminded that shields drop faster to energy weapons and that there are many different ways to kill your enemies.
Regarding story elements, this entry in the Halo series does a great job at narrating events on Reach. You are a Spartan soldier taking the place as replacement for a lost soldier in Noble Team. You are Noble Six. You start with straightforward missions and otherwise easy enough objectives to get accustomed to the new things. But after the first few events the story develops in an amazing way, and giving you hints and little pieces of information that make you feel much more accomplished about your actions. The events that take place feel much more meaningful in the way that you actually feel like you made things happen and you want to find out what happens next. Throughout the campaign your link with the spartan you created at the beginning is reinforced.
And in the end, once you have finally finished the epic campaign, you have the greatly varied and entertaining multiplayer. With many different options to satisfy anyone's preferences, varied gameplay, voting to choose a game, customization and many other things, the multiplayer does a great job at what it is expected to do and much more. Instead of experience points you gain credits, which you can spend to even further customize your Spartan. Moreover, the addition of daily and weekly challenges keep your gameplay varied and help post goals for the day.
Halo: Reach is a good, solid game, but most importantly a complete game.