I wrote a post a few days ago on how Polish verbs are hard to learn. I wanted to expand on what I wrote earlier, and include some examples.
First of all, when you are learning a Polish verb, you are usually not learning just one verb, but two verbs. One is imperfective and the other is perfective. You have to not only wrap your head around the difference in aspect, you have to learn two different words. Sometimes they can be totally different, as in "widzieć, zobaczyć" (to see), or "brać, wziąć" (to take). Sometimes they are just formed by adding a prefix to the other one in the pair, which can add a new level of complexity if other verbs with different meaning exist with similar prefixes. Sometimes they have a different ending, as in "unikać, uniknąć" (to elude, escape). Sometimes there are more than two verbs to learn, as in "zgadywać/odgadywać, zgadnąć/odgadnąć" (to guess), or "sprzątać, sprzątnąć/posprzątać/wysprzątać" (to tidy up).
And to top it off, there are different shades of meaning for different words which may not necessarily overlap across varied languages. For example, in English, "make" can mean "to commit" (popełniać, popełnić), "to accomplish" (dokonywać, dokonać), "to produce" (wykonywać, wykonać) "to create" (tworzyć, utworzyć), "to act" (czynić, uczynić), "to do" (robić, zrobić), as well as being secondarily implicated in some unit of meaning such as "make sense," "make fun of," "make use," "make do," "make love," "make up," "make trouble," "make sure," etc.
Then you have to learn the various ways that they conjugate, which ones are irregular, which ones end in "c" instead of "ć," what case they take, etc. It becomes apparent quickly that thinking in Polish is a lot different from thinking in English.