Public demo starts tomorrow. For now, here's the second part of my thoughts on the demo. I did a playthrough with the conversations set to play automatically as cutscenes. The default options were a mix of paragon and renegade, seemingly based on Shepard's mood. I also played through a couple times on insanity.
Insanity is going to be extremely comp based. Damage powers like warp felt very very weak, and enemies seemed to be impossible to solo outside of cover without using a power. Being shot at outside of cover basically means you get instagibbed. I played as a vanguard first, and I felt like every power was useless. Nova was an easy way to kill yourself, so was biotic charge. Shockwave was difficult to land on CC'd targets. Pull was the only ability that I actually got any good use out of, but it still felt quite underpowered. Why did it feel underpowered? Singularity is why. Every combat basically came down to spamming Liara's singularity. Most enemies had no tech/biotic protection, and singularity was simply the safest way to dps enemies. Enemies that had shields were the biggest problems by far. Overload had an extremely long CD, and didn't do enough damage. Once again though, Liara saved the day. Stasis could be used even on shielded targets, and unlike in ME1, enemies could be damaged in it.
Overall, I don't see the hybrid classes being very useful, except for possibly the Sentinel, and even then only as an overload bot. The main problem with the hybrid classes is that their CDs were far too long. Garrus' overload was about a 13 second CD, while Liara's powers were about a 6 second CD, and I still had more CD reduction to pick up. The boss at the end of the demo played a little differently. Guns seemed almost useless against it. It took 1-2 clips of ammo to take away about 1 shield/armor segment, (10 segments makes a whole bar) overload and warp were both pretty useful though. Overload would do enough damage to take away one segment from shields or armor, and warp would do 1 segment of damage to armor. In general, guns seemed to only be used to pick at the boss while waiting for powers to CD, or as cleanup for normal enemies.
I think the best comp by far will be soldier Shepard, with Liara and Tali. For my soldier I will probably use disruptor ammo, as it seems like shields are the most problematic form of protection. I could also see replacing Tali with a sentinel, like Kaiden. If you're playing an adept, sentinel, or engineer, I wouldn't recommend trying to "balance" out your team comp by using a combat or hybrid combat character. Squadmates are only good when they're using powers, and they tend to just do stupid things with guns, and they just don't do as much damage as the player. I think Liara and Tali, or Liara and Kaiden will simply be the best party members for insanity, because CC is just too powerful. Maybe soldier type characters will feel more powerful with better weapons and upgrades, as I had a distinct lack of Revenant+Viper in the demo.
Also, grenades fucking hurt!