Drawback of ElGamal encryption I am trying to find out some disadvantages of ElGamal cryptography but I'm not able to figure out what's wrong with the algorithm. The only one I found is that a known-plain text attack is possible in ElGamal if the same $r$ is used twice during encryption.

Are there any other disadvantages of ElGamal encryption?
ElGamal is a scheme, that can be applied to any kind of group structure. The only requirement is that DDH has to be hard (e.g. not $(\mathbb{Z}_p,+)$).

If you use the most common construction with multiplicative groups $(\mathbb{Z}_p^*,\cdot)$, then you need larger groups, due to attacks like index calculus.

If you use elliptic curves, you can use smaller groups instead, because algorithms like index calculus are not known.

Elliptic curves with pairings are not suitable to be used, because in that case the DDH problem is not hard. Therefore, you can not design protocols with efficiently computable pairings. 

One property of ElGamal is, that it is (semi-)homomorphic w.r.t. the group operation. If you see that as an unwelcome property, you can also call that malleable. If you consider this property useful or a security risk, depends on your point of view and your actual goal.