Better than the first, but a a lot harder
The game play is extremely similar to the first game with some major improvements. The biggest addition is the ability to dual wield weapons, using the left and right trigger buttons. The only drawback is that you cannot use grenades when you dual wield, so depending on the situation, you may have to do away with one of the weapons and use a grenade. Another major game play change is to the health meter. In the game all you have is the shield and no underlying health meter, meaning that once your shield is gone, you can only take a few hits before your killed. This will cause you to look for cover more and to be more cautious.
Once again in Halo, you are offered a wide array of weapons both Covenant and Human. You have several cool new weapons in addition to the ones seen in the first game, like the energy sword (first seen in Halo) that delivers an extraordinary amount of damage and will become your favorite weapon in the game, especially against The Flood. You also have the SMG, which alone is useless but dual wield them and you'll have a pretty effective weapon. Unfortunately, the pistol now sucks and is completely useless in this game and the rifle is god awful also. Prepare to use more Covenant weapons than human weapons.
There is also a wide array of new vehicles also in addition to the ones seen in the first game. On the human side, there is the Scorpion, a massive tank that deals an impressive amount of damage but is slow as slow can be. On the Covenant side you have the inclusion of the Spectre, which is like the Warthog of the Covenant. Unlike the first game, the vehicles have no health meter, so you'll have to guesstimate how much damage they have taken before they're completely useless, although how much damage they've taken is shown on the actual machine itself. The bright side about vehicles this time around is like the Warthog and the Spectre, you don't have to drive them and you can take the fun jobs like being on the turret.
The friendly AI is much improved from the first game, but that also means that the enemy AI is harder as well, especially the Flood. The Flood (shortly followed by The Brutes) will serve as the biggest thorn in your side the entire game. The Flood don't stop coming and they take forever to kill, so it will be more beneficial to run than to try and fight them off.
Some of these new factors make the game a lot more challenging, but once you get the hang of these new challenges, the game will be a lot of fun. If the cliffhanger ending ruined the game for you, I can understand, I was a little peeved too.