Yes, she is rather weak at the begining of the game. She's a carry. But if you buy Mejai's Soulstealer as soon as you can, get some kills or assists in and don't die, you will dominate. Soulstealer + Archangels Staff + Deathfiregrasp = dominance.
Use CD reduction runes and spec 9-0-21, you will be able to fire off your ult about every 15 sec that will do around 900+ dmg. Most champs will have around 2k health at late game. In other words, you're able to knock off half their health every 15 sec. Not only that, but you'll be able to use your snare and your slow every few sec that will also do a decent amount of damage.
All in all, people who want to play as Lux need a lot of practice with her. She is one of the most difficult champions to play, but can be one of the most powerful if you know how to play her.
A Buyer's Guide to League of Legends: Lux
While Lux is definitely one of the most fun champions to come to the League of Legends, can she really contribute at the higher levels?
When I first heard about the mechanics behind League of Legends' latest champion, Lux, the Lady of Luminosity, I'll admit that I was more excited to play her than what warrants my normal response to a champion release. A week prior to Lux's arrival, I had managed to convince a former competitive gaming partner of mine to play League of Legends, and so we were going through the process of finding a solid champion duo to play. He prefers to play strong physical DPS champions, so I advised him to start out with Tristana, a powerful ranged carry who, with a little bit of support from her team, remains effective at all stages of the game. Now, like any of the defensively squishy ranged DPS champions, Tristana synergizes best with someone who can protect her back with stuns or snares so that she can maintain her offensive positioning. Originally, I had been playing Morgana as my complimentary support champion, but since I've been a consistent Morgana player since closed beta, for well over a year now, I was really craving a new champion who played similar to my favorite fallen angel.
Enter Lux, a purportedly strong support champion with a powerful skill-shot snare ability, similar to Morgana's 'Dark Binding' snare spell, but with a faster travel speed and the ability to hit up to two targets in a line. Lux's other spells are also thematically similar to Morgana's, like her damage shield, "Prismatic Barrier," which fires out like a boomerang, buffing her teammates, and Lux herself, up to two times when coming in contact with her spell. Lux's last regular skill, "Lucent Singularity," is an interesting AoE-slowing ability that allows Lux to place a glowing orb of light in an area, causing any enemy champion who comes in contact with the orb to be instantly slowed by up to 30%, and Lux has the option to prematurely pop the Orb to deal a moderate amount of magic damage. Finally, Lux's ultimate, Finales Funkeln, is one of the most fun abilities I have ever seen in League of Legends; similar to Ashe's global Enchanted Crystal Arrow ult, Lux charges up her laser for a second before firing off a long-range concentrated beam, dealing solid damage to everyone caught.
On paper, all of these abilities sound really great and, in execution, they're definitely a lot of fun to play with. I noted earlier that Lux reminds me a lot of Morgana in the way her skills are set up, but to focus more on the contrasts between the two, Lux definitely plays like a more mobile long-ranged version of Morgana. Good Morgana players tend to add some tanking items to their repertoire to get the full effect of her ultimate in the midst of her enemies, but Lux is quite capable of supporting and dealing damage from the back lines. Since I was playing Lux in the same role as Morgana (supporting the carry and dealing damage), I just followed my Tristana friend around the map, utilizing my abilities to keep enemies at bay.
Sadly, while Lux is definitely a lot of fun to play, she has fallen under a lot of player criticism for simply being underwhelming in her overall execution and, I hate to say it, I agree. The real difficulty with Lux stems from two problems: the first, in having a bad synergy between her champion design and her passive ability, and the second problem being that her abilities are all, relatively speaking, weak and somewhat low in utility.
To deal with the first problem, Lux's passive, "Illumination," places a debuff on any enemy champion that she deals magic damage to, and if Lux hits them with a physical attack, she can "pop" the debuff, instantly dealing an extra 20-190 magic damage to the target. The problem here is that Lux's ability casting range is much further than her attacking range, so smart Lux players who try to capitalize on her passive end up being punished for moving in so close. Lux is meant to be played at a long distance away from the main fight, and in the many games where I attempted to utilize her passive (buying Sheen to Lich Bane), placing myself in a close enough proximity to attack often left me out of position and in more danger than was necessary. Unfortunately, it seems that much of Lux's damage potential was designed with her constantly utilizing her passive ability, and so her spells are, in comparison, weaker than most.