Pros
ASM is an ethical company with a not yet overwhelming bureaucracy. The environment tends perhaps to be somewhat less political than at other companies. The work is generally interesting although frequent (perhaps unnecessary) fire drills sometimes taint the work environment a bit. The salary and benefits are decent.
Cons
Unless you are in the Netherlands, your opportunities for advancement are limited. This is especially true for technical employees not interested in management (this problem is of course not unique to ASML). The employee ranking system pretends to foster career development but does not. There is limited opportunity for top-performers outside of management to be compensated accordingly since the ranking system is designed to cluster everyone towards average.