I would be hard-pressed to analyze why Metro Last Light feels slightly flat, but it does. There's really nothing much to complain about. The story is adequate, the graphics are great, the visuals are good, the mechanics work, particularly the stealth that was a problem in the last game. I've struggled to put my finger on it and the only thing I can think of has to do with the actual story. Metro 2033 was a much more dramatic experience. It was all about life and death survival in the aftermath of the apocalypse whereas Last Light is a lot more mundane, dealing mostly with old fashioned politics and the struggles for power between various factions. The concentration here is on the human enemies and less on the creatures, which turns Last Light into something quite different than its predecessor. It's morphed from a horror survival experience into a shooter with more typical enemies in the form of warring factions, nazis, communists and bandits. Although, it's probably more realistic in the sense of what would actually happen after the urgency of a disaster passes, it doesn't make for a uniquely exciting game plot.
The same protagonist returns in this sequel and carries on the storyline from Metro 2033, but with Artyom now officially a Ranger and under the command of Colonel Miller. The story presumes the previous bad ending, and re-iterating Artyrom's connection to the Dark Ones that was established in the first game, his orders are to find the last surviving Dark One and kill it in the belief it poses a major threat. Artyom, however, has his own motives and is not exactly on-board with the plan. He is haunted by visions of his mass killing of those that only sought peace. Although this is the underlying plot, Artyom's interactions are mostly with the human obstacles and less with creatures. Alhough the game does have its sequences when Artyom must deal with them, they are no longer the main antagonists.
There were lots of complaints and frustrations with stealth in Metro 2033 and this mechanic has been much improved, but it also makes the game easier to kill enemies or just sneak past them. You can stealth your way fairly easily the whole way. Your safe zone has vastly increased and you can practically waltz by the enemy or easily sneak up behind a lot of them, although sometimes it seems like they can see you in the dark or at least hear you. Here, you never truly feel that the hero is in much danger and the closest thing to some tension is the spiders and the outdoor experience where creatures lurk and the atmosphere is creepy. If you explore and manage your inventory well, there is also no shortage of filters or ammo, which removes any sense of urgency or panic. In fact, if you go stealth, you will likely have an overabundance.
As previously, the game has two possible endings depending on moral points, which are gained by not killing anyone in certain segments. So, if you just want to collect the notes in these sections, it's not necessary to engage anyone. Although ammo is not a big problem regardless of which way you go, you hardly need to replace any in stealth mode. In order to gain moral points, listen to all conversations till the end of them, watch any shows, such as shadow and theatre, explore all dead ends and alcoves and save the prisoners from the bandits. Once hooking up with the Dark One, listen to his comments about certain creatures not being dangerous if not antagonized. Of course there is no indication in game concerning all of this and you can only be aware by reading up on it beforehand, which kinda spoils the experience. However, I suspect it entices you to play the game twice to get the alternate ending.
Some bosses can be a little unbalanced, for instance if you get caught without much air at the church, you have no chance of making it as the Amphybian takes a lot of damage to kill. There is simply no alternative. You need at least 3.00 minutes of filter time. However, with a little better management, you can end up with an abundance of gas masks. Just be sure to explore to collect them. Killing is the harder way to go in terms of gas masks because you need to kill in order to fully explore areas and therefore you use more air.
Another area is an ammo problem at the boss in the catacombs if you don't buy the max at the church. However, here you do have an option if you have him break all the pillars and the only ammo you need is to kill a couple of watchmen and finish him off with a couple of shots. Make sure to check bodies twice for loot as often everything available does not show up right away.
Although the graphics are good, the creatures are not so well-defined as in Metro 2033 and harder to see due to motion blur. You can try turning the settings down for this. Another problem is losing voice volume if you turn away from the speaker.
In summary, although Last Light is beautiful to look at and mechanically sound, there is just not the tension of the first game and the high emotional drama is missing. Ammo and filters are abundant, Artyom is much more skilled, and the stealth mechanics are heavily weighted in favor of your character. I imagine this is in response to the complaints against Metro 2033. However, in "fixing" these, it has gone too far in the opposite direction and things are just a bit too easy. That is not to say it's a bad game, it's actually quite a good game. It's just not a "great" game, which I feel the first one was. Metro 2033 was damned difficult, but survival against the odds should be and horror should be horrifying.
I'm also not a big fan of stealth mode, but seem to be running across a few of them that offer this option on how to play. I quite frankly lack the patience to wait things out for the opportunity to move forward, but also don't find this mechanic to be as much fun as blasting my way through a game. Getting a good ending through letting the bad guys live, however, seems to be a trend and I can see how it gives a game greater options for the player. I mean, everyone prefers a good ending, right?