However, it has a ton of curious rules (called sandhi) to join adjacent words into one unit, with various changes at the boundaries of the words. For instance, nara(h) tatra ("[a] man [is] there") = narastatra (without spaces and pauses in speech). So in this way, a whole sentence can be written as just one "word", with a bunch of weird changes in the middle. (Also the fact that it's written using a script that has 1 character per syllable does not help, because the words generally join one another "in the middle of a character".) So it sometimes happens that you split the mess in a wrong way, then spend half an hour trying to translate the thing, and then your teacher shows you another splitting that leads to an immediate and simple translation.

Second, it has some crazy composites. It's like German, only several times worse, especially when it comes to composites that just mean several things together. A typical example (with a bad transliteration, so that you can more easily read it ): mrgavyaghrasimharksagajapurne vane = in a forest (vane) full (purne) of gazelles (mrga), tigers (vyaghra), lions (simha), bears (rksa) and elephants (gaja).

And third, it's probably the only language that I know of which has a lot of nouns with several roots. Many words have three of them, like the well-known word "raja": there is the strong root (rāja-), the middle root (rājā-) and the weak root (rajňā-). Each of these roots is used only in certain cases (with number and gender included), so for instance, in singular, masculine and feminine nouns use the strong root for nominative and accusative, but the neuter nouns use the middle root for them; and all of them use the weak root for the other cases. (And it gets more complicated with the other numbers. )

And to make it even worse, it has an awful lot of words. In English, one word has pretty much always more than one meaning, so you don't need to know a whole lot of words. In Czech, the relationship is pretty much 1:1. But in Sanskrit, it's more like 5 words for any single meaning. When I was learning, I knew no less than 6 words for a "king", for instance, all of them being used interchangeably. (And the situation was the same even for some weird words, like "arrow" — I think I knew 3 words for that, now I can recall only two.)

(And then there are the awesome pieces of Sanskrit wisdom. I used to encounter at least one bit each week. Sentences like "Whoever mounts a tiger, a donkey, a camel, and/or a buffalo, will certainly die within six months" always had me laughing hard. (By the way, all the animals are a single composite, so it's actually not at all clear if you need to mount all four, or only one in order to die.))

I guess this is a bit in the same vein as the English words "awesome" and "awful". Both of those seem to derive from the same word "awe", and still they have totally opposite meanings.

Also, I have seen the word "aweful" used in the sense of awe-inspiring, but if my memory serves me rightly, it was in an 18th-century description of the then newly rebuilt St Paul's Cathedral. "Aweful" with that spelling is not given in the dictionary that I use most often (Chambers Dictionary), but it does give awe-inspiring as an alternative meaning for "awful".